Adding image based on background color in angular

If your background color is applied from a stylesheet rule, you can get its value by reading element computed style.

Here is a stackblitz example which add the string "(This item is red)" after item value if the element background color is red.
You can apply this logic to your case by replacing the string by an image.

component

export class AppComponent  {
  items = [
    'item 1',
    'item 2',
    'item 3'
  ];

  isRed(element)
  {
    var color = window.getComputedStyle(element).getPropertyValue("background-color");
    return color === 'rgb(255, 0, 0)';
  }
}

template

<ul>
  <li *ngFor="let item of items" #itemRef>
    {{item}}
    <span *ngIf="isRed(itemRef)">(This item is red)</span>
  </li>
</ul>

stylesheet

li:nth-child(1) {
  background-color: red;
}

li:nth-child(2) {
  background-color: green;
}

li:nth-child(3) {
  background-color: blue;
}