A great way to hone your color and design skills is to draw a few shapes on the computer, assemble them in a design form and then color them.
Here I have drawn a circle, triangle and square, all done in line on the computer. You could also draw freehand shapes instead of mechanical ones.
Above I have assembled them into a design, shown are four different possibilities, although many more could be created.
I add colors using the Paint Bucket Tool.
Countless variations are possible, just have fun.
Here I have pulled the designs together by just adding a black background. This is an interesting way to experiment with design and color.