You don't need to add to percentage here, you're already doing it in AAColorMyApp.m.
Percentage must between 0.0 and 1.0, but we're adding 0.1 to it.

In order to keep the value at (or below) 1.0, we must subtract
1.0 from it whenever it goes over 1.0.
Set the background color of the grayscale color bar.

The reason your grayscale color bar stayed white, no matter what...
was that your code wasn't setting your [UIColor white...] return
value to the background color.
Merge pull request #1 from mudphone/caseymorrissey

I've fixed a couple of things that will make the color change a little smoother. Also, I removed duplicate work.