Cannot change the color of part of my 2D UI

Hello, as you can see the color should be set to red for my 2D slider, but it won’t change. I imported a circle from photoshop which was colored black, so I’m not sure if that’s why it won’t change color. Any help would be greatly appreciated.

Color is added to the surface you provide. It’s like putting red tint glass on a black surface, in final you see only black. Make your 2D slider a light color.