Add gradient color layer on photo and make it with a special effect.
Create assets with gradient color for your art creation.

Quick Guide:
.Tap on Plus button to add colors
.Tap on empty zone of image to show or hide buttons
.Tap on color tile to select or deselect
.Pan selected color-tile(s) onto another tile to rearrange colors
.Pan selected color-tile(s) onto Trash-can icon to delete
.Pan selected color-tile(s) onto Dropper icon to change color(s)
.Drag the blue or red point to adjust angle of gradient color

The iOS/macOS version of this app are both available in App Store.