7 files declare their use of Color in Drupal 8

color.module in core/modules/color/color.module

Allows users to change the color scheme of themes.

Color.php in core/lib/Drupal/Core/Render/Element/Color.php

ColorTest.php in core/tests/Drupal/Tests/Component/Utility/ColorTest.php

CreateNew.php in core/modules/system/src/Plugin/ImageToolkit/Operation/gd/CreateNew.php

GDToolkit.php in core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php

Rotate.php in core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Rotate.php

RotateImageEffect.php in core/modules/image/src/Plugin/ImageEffect/RotateImageEffect.php