ios中的渐变颜色太亮

import UIKit

// 创建渐变图层
let gradientLayer = CAGradientLayer()
gradientLayer.frame = view.bounds

// 设置渐变颜色
let startColor = UIColor.red
let endColor = UIColor.yellow
gradientLayer.colors = [startColor.cgColor, endColor.cgColor]

// 调整颜色亮度
let darkerStartColor = adjustBrightness(color: startColor, brightness: 0.8)
let darkerEndColor = adjustBrightness(color: endColor, brightness: 0.8)
gradientLayer.colors = [darkerStartColor.cgColor, darkerEndColor.cgColor]

// 添加渐变图层到视图
view.layer.addSublayer(gradientLayer)

// 调整颜色亮度的函数
func adjustBrightness(color: UIColor, brightness: CGFloat) -> UIColor {
    var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
    color.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
    
    return UIColor(red: red * brightness, green: green * brightness, blue: blue * brightness, alpha: alpha)
}