Angular 7-根据条件更改Mat-select-值的颜色

<mat-form-field>
  <mat-select [(ngModel)]="selectedValue">
    <mat-option value="option1">Option 1</mat-option>
    <mat-option value="option2">Option 2</mat-option>
    <mat-option value="option3">Option 3</mat-option>
  </mat-select>
</mat-form-field>

import { Component } from '@angular/core';

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html',
  styleUrls: ['./example.component.css']
})
export class ExampleComponent {
  selectedValue: string;

  getOptionClass(): string {
    if (this.selectedValue === 'option1') {
      return 'option1-color';
    } else if (this.selectedValue === 'option2') {
      return 'option2-color';
    } else if (this.selectedValue === 'option3') {
      return 'option3-color';
    } else {
      return '';
    }
  }
}

.option1-color {
  color: red;
}

.option2-color {
  color: blue;
}

.option3-color {
  color: green;
}