颜色 | <color>

The <color> CSS data type represents a color in the sRGB color space. A color can be described in any of the following ways:

• using a keyword
• using the RGB cubic-coordinate system (via the #-hexadecimal or the rgb() and rgba() functional notations)
• using the HSL cylindrical-coordinate system (via the hsl() and hsla() functional notations)

A color value may also include an alpha-channel transparency value, indicating how the color should composite with its background.

Although CSS color values are precisely defined, their appearance may vary (sometimes significantly) from device to device. This is because most devices are not calibrated, and some browsers do not support output devices' color profiles.

This article describes the color data type in detail. For a look at using color in HTML, see Applying color to HTML elements using CSS.

Accessibility note: Some people have difficulty distinguishing colors. The WCAG 2.0 recommendation strongly advises against using color as the only means of conveying a specific message, action, or result. (See Color and color contrast for more information.)

Interpolation

In animations or <gradient>s, color values are interpolated on each of their red, green, and blue components. Each component is handled as a real, floating-point number. Note that interpolation of colors happens in the alpha-premultiplied sRGBA color space to prevent unexpected gray colors from appearing. In animations, the interpolation's speed is determined by the timing function.

Values

There are several ways to describe a <color> value.

Color keywords

Color keywords are case-insensitive identifiers that represent a specific color, such as red, blue, brown, or lightseagreen. The name describes the color, though it is mostly artificial. The list of accepted values has varied a lot throughout the different specifications:

• CSS Level 1 only accepted 16 basic colors, called the VGA colors as they were taken from the set of displayable colors on VGA graphics cards.
• CSS Level 2 added the orange keyword.
• Although various colors not in the specification (mostly adapted from the X11 colors list) were supported by early browsers, it wasn't until SVG 1.0 and CSS Colors Level 3 that they were formally defined. They are called the extended color keywords, the X11 colors, or the SVG colors.
• CSS Colors Level 4 added the rebeccapurple keyword to honor web pioneer Eric Meyer.

There are a few caveats to consider when using keywords:

• Except for the 16 basic colors, color keywords can only be used in CSS and SVG. HTML does not recognize them and will use a specific algorithm to convert them to completely different colors.
• Unlike HTML, CSS will completely ignore unknown keywords.
• No keyword-defined colors in CSS have any transparency—they are plain, solid colors.
• Several keywords denote the same colors:
  • aqua / cyan
  • fuchsia / magenta
  • darkgray / darkgrey
  • darkslategray / darkslategrey
  • dimgray / dimgrey
  • lightgray / lightgrey
  • lightslategray / lightslategrey
  • gray / grey
  • slategray / slategrey
• Though many keywords have been adapted from X11, their RGB values may differ from the corresponding color on X11 systems since manufacturers sometimes tailor X11 colors to their specific hardware.

transparent keyword

The transparent keyword represents a fully transparent color. This makes the background completely visible. Technically, transparent is a shortcut for rgba(0,0,0,0).

Compatibility note: To prevent unexpected behavior, such as in <gradient>s, the current W3C spec states that transparent should be calculated in the alpha-premultiplied color space. However, be aware that older browsers may treat it as black with an alpha value of 0.

Historical note:transparent wasn't a true color in CSS Level 2 (Revision 1). It was a special keyword that could be used instead of a regular <color> value on two CSS properties: background and border. It was essentially added to allow developers to override an inherited solid color. With the advent of alpha channels in CSS Colors Level 3, transparent was redefined as a true color. It can now be used wherever a <color> value can be used.

currentColor keyword

The currentColor keyword represents the value of an element's color property. This lets you use the color value on properties that do not receive it by default.

CurrentColor example

rgb() and rgba()

Note: As of CSS Colors Level 4, rgba() is an alias for rgb(). In browsers that implement the Level 4 standard, they accept the same parameters and behave the same way.

Colors can be defined according to their red, green, and blue components (the RGB model) by using hexadecimal and functional notations. The optional alpha component represents transparency.

Syntax

Hexadecimal notation: #RRGGBB[AA]R (red), G (green), B (blue), and A (alpha) are hexadecimal characters (0-9, A-F). A is optional. For example, #ff0000 is equivalent to #ff0000ff.Hexadecimal notation: #RGB[A]R (red), G (green), B (blue), and A (alpha) are hexadecimal characters (0-9, A-F). A is optional. The three-digit notation (#RGB) is a shorter version of the six-digit form (#RRGGBB). For example, #f09 is the same color as #ff0099. Likewise, the four-digit RGB notation (#RGBA) is a shorter version of the eight-digit form (#RRGGBBAA). For example, #0f38 is the same color as #00ff3388.Functional notation: rgb(R, G, B[, A]) or rgba(R, G, B, A)R (red), G (green), and B (blue) can be either <integer>s or <percentage>s, where the number 255 corresponds to 100%. A (alpha) can be a <number> between 0 and 1, or a <percentage>, where the number 1 corresponds to 100% (full opacity).

Examples

RGB example

RGBa example

hsl() and hsla()

Note: As of CSS Colors Level 4, hsla() is an alias for hsl(). In browsers that implement the Level 4 standard, they accept the same parameters and behave the same way.

Colors can be defined according to their hue, saturation, and lightness (the HSL model) via the hsl() and hsla() functional notations. One advantage of HSL over RGB is that it is more intuitive: you can guess at the color you want, and tweak it from there. It is also easier to create a set of matching colors (e.g., by keeping the hue the same, while varying the lightness/darkness and saturation).

Syntax

Functional notation: hsl(H, S, L[, A]) or hsla(H, S, L, A)H (hue)is an <angle> of the color circle given in degs, rads, grads, or turns. When written as a unitless <number>, it is interpreted as degrees. By definition, red=0deg=360deg, with the other colors spread around the circle, so green=120deg, blue=240deg, and so on. As an <angle>, it implicitly wraps around such that -120deg=240deg, 480deg=120deg, -1turn=1turn, etc.S (saturation) and L (lightness) are percentages. 100%saturation is completely saturated, while 0% is completely unsaturated (gray). 100%lightness is white, 0% lightness is black, and 50% lightness is “normal.”A (alpha) can be a <number> between 0 and 1, or a <percentage>, where the number 1 corresponds to 100% (full opacity).

Examples

HSL example

Fully saturated colors

Lighter and darker greens

Saturated and desaturated greens

HSLa example

System Colors

Not all system colors are supported on all systems. for use on public web pages.

ActiveBorderActive window border.ActiveCaptionActive window caption. Should be used with CaptionText as foreground color.AppWorkspaceBackground color of multiple document interface.BackgroundDesktop background.ButtonFaceFace background color for 3-D elements that appear 3-D due to one layer of surrounding border. Should be used with the ButtonText foreground color.ButtonHighlightThe color of the border facing the light source for 3-D elements that appear 3-D due to that layer of surrounding border.ButtonShadowThe color of the border away from the light source for 3-D elements that appear 3-D due to that layer of surrounding border.ButtonTextText on push buttons. Should be used with the ButtonFace or ThreeDFace background color.CaptionTextText in caption, size box, and scrollbar arrow box. Should be used with the ActiveCaption background color.GrayTextGrayed (disabled) text.HighlightItem(s) selected in a control. Should be used with the HighlightText foreground color.HighlightTextText of item(s) selected in a control. Should be used with the Highlight background color.InactiveBorderInactive window border.InactiveCaptionInactive window caption. Should be used with the InactiveCaptionText foreground color.InactiveCaptionTextColor of text in an inactive caption. Should be used with the InactiveCaption background color.InfoBackgroundBackground color for tooltip controls. Should be used with the InfoText foreground color.InfoTextText color for tooltip controls. Should be used with the InfoBackground background color.MenuMenu background. Should be used with the MenuText or -moz-MenuBarText foreground color.MenuTextText in menus. Should be used with the Menu background color.ScrollbarBackground color of scroll bars.ThreeDDarkShadowThe color of the darker (generally outer) of the two borders away from the light source for 3-D elements that appear 3-D due to two concentric layers of surrounding border.ThreeDFaceThe face background color for 3-D elements that appear 3-D due to two concentric layers of surrounding border. Should be used with the ButtonText foreground color.ThreeDHighlightThe color of the lighter (generally outer) of the two borders facing the light source for 3-D elements that appear 3-D due to two

concentric layers of surrounding border.ThreeDLightShadowThe color of the darker (generally inner) of the two borders facing the light source for 3-D elements that appear 3-D due to two

concentric layers of surrounding border.ThreeDShadowThe color of the lighter (generally inner) of the two borders away from the light source for 3-D elements that appear 3-D due to two concentric layers of surrounding border.WindowWindow background. Should be used with the WindowText foreground color.WindowFrameWindow frame.WindowTextText in windows. Should be used with the Window background color.

Mozilla System Color Extensions

-moz-ButtonDefaultThe border color that goes around buttons that represent the default action for a dialog box.-moz-ButtonHoverFaceThe background color of a button that the mouse pointer is over (which would be ThreeDFace or ButtonFace when the mouse pointer is not over it). Should be used with the -moz-ButtonHoverText foreground color.-moz-ButtonHoverTextThe text color of a button that the mouse pointer is over (which would be ButtonText when the mouse pointer is not over it). Should be used with the -moz-ButtonHoverFace background color.-moz-CellHighlightBackground color for selected item in a tree widget. Should be used with the -moz-CellHighlightText foreground color. See also -moz-html-CellHighlight.-moz-CellHighlightTextText color for a selected item in a tree. Should be used with the -moz-CellHighlight background color. See also -moz-html-CellHighlightText.-moz-Combobox Background color for combo-boxes. Should be used with the -moz-ComboboxText foreground color. In versions prior to 1.9.2, use -moz-Field instead.-moz-ComboboxText Text color for combo-boxes. Should be used with the -moz-Combobox background color. In versions prior to 1.9.2, use -moz-FieldText instead.-moz-DialogBackground color for dialog boxes. Should be used with the -moz-DialogText foreground color.-moz-DialogTextText color for dialog boxes. Should be used with the -moz-Dialog background color.-moz-dragtargetzone-moz-EvenTreeRow Background color for even-numbered rows in a tree. Should be used with the -moz-FieldText foreground color. In Gecko versions prior to 1.9, use -moz-Field. See also -moz-OddTreeRow.-moz-FieldText field background color. Should be used with the -moz-FieldText foreground color.-moz-FieldTextText field text color. Should be used with the -moz-Field, -moz-EvenTreeRow, or -moz-OddTreeRow background color.-moz-html-CellHighlight Background color for highlighted item in HTML <select>s. Should be used with the -moz-html-CellHighlightText foreground color. Prior to Gecko 1.9, use -moz-CellHighlight.-moz-html-CellHighlightText Text color for highlighted items in HTML <select>s. Should be used with the -moz-html-CellHighlight background color. Prior to Gecko 1.9, use -moz-CellHighlightText.-moz-mac-accentdarkestshadow-moz-mac-accentdarkshadow-moz-mac-accentface-moz-mac-accentlightesthighlight-moz-mac-accentlightshadow-moz-mac-accentregularhighlight-moz-mac-accentregularshadow-moz-mac-chrome-active-moz-mac-chrome-inactive-moz-mac-focusring-moz-mac-menuselect-moz-mac-menushadow-moz-mac-menutextselect-moz-MenuHoverBackground color for hovered menu items. Often similar to Highlight. Should be used with the -moz-MenuHoverText or -moz-MenuBarHoverText foreground color.-moz-MenuHoverTextText color for hovered menu items. Often similar to HighlightText. Should be used with the -moz-MenuHover background color.-moz-MenuBarText Text color in menu bars. Often similar to MenuText. Should be used on top of Menu background.-moz-MenuBarHoverTextColor for hovered text in menu bars. Often similar to -moz-MenuHoverText. Should be used on top of -moz-MenuHover background.-moz-nativehyperlinktext Default platform hyperlink color.-moz-OddTreeRow Background color for odd-numbered rows in a tree. Should be used with the -moz-FieldText foreground color. In Gecko versions prior to 1.9, use -moz-Field. See also -moz-EvenTreeRow.-moz-win-communicationstext Should be used for text in objects with -moz-appearance: -moz-win-communications-toolbox;.-moz-win-mediatext Should be used for text in objects with -moz-appearance: -moz-win-media-toolbox.-moz-win-accentcolorRequires Gecko 56

Used to access the Windows 10 custom accent color that you can set on the start menu, taskbar, title bars, etc.-moz-win-accentcolortextRequires Gecko 56

Used to access the color of text placed over the Windows 10 custom accent color in the start menu, taskbar, title bars, etc.

Mozilla Color Preference Extensions

-moz-activehyperlinktextUser's preference for text color of active links. Should be used with the default document background color.-moz-default-background-color User's preference for the document background color.-moz-default-color User's preference for the text color.-moz-hyperlinktextUser's preference for the text color of unvisited links. Should be used with the default document background color.-moz-visitedhyperlinktextUser's preference for the text color of visited links. Should be used with the default document background color.

Specifications

Browser compatibility

1 The 'e'-grey colors (with an e) (grey, darkgrey, darkslategrey, dimgrey, lightgrey, and lightslategrey) are only supported since IE 8.0. IE 3 to IE 7 only support the 'a' variants: gray, darkgray, darkslategray, dimgray, lightgray, and lightslategray.

2 IE 7-8 supports the transparent keyword only for background and border. color: transparent; is drawn black in IE. IE6 renders transparent borders as black, as well.

3 This feature is supported since Chrome 52.0 behind the "Experimental Web Platform features" flag in chrome://flags. See Chromium bug 76362.

4 This feature is supported Opera 39.0 behind the "Enable experimental Web Platform features" flag in chrome://flags.

See also

• The opacity property lets you define transparency at the element level.
• The color, background-color, border-color, outline-color, text-shadow, box-shadow properties.

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https://developer.mozilla.org/en-US/docs/Web/CSS/color_value