docs(material/list): Update description for color input description on API page (angular#29327)

Author: amysorto

src/material/list/list-option.ts

@@ -129,7 +129,13 @@ export class MatListOption extends MatListItemBase implements ListOption, OnInit
     this.togglePosition = value;
   }
 
-  /** Theme color of the list option. This sets the color of the checkbox/radio. */
+  /**
+   * Theme color of the list option. This sets the color of the checkbox/radio.
+   * This API is supported in M2 themes only, it has no effect in M3 themes.
+   *
+   * For information on applying color variants in M3, see
+   * https://material.angular.io/guide/theming#using-component-color-variants.
+   */
   @Input()
   get color(): ThemePalette {
     return this._color || this._selectionList.color;