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

1) You don't need to add 0.1 to percentage twice.
2) You can subtract 1.0 from newPercentage whenever it is greater than 1.0 for a smoother color transition.
3) You grayscale color bar wasn't changing color because AAGrayscaleView was missing an assignment to self.backgroundColor.