If you've worked on commercial project, you know there's only one constant: change… especially at the last minute. One of the things that seems to frequently change is color choice. If you have a complicated AE animation and many layers that use the same colors, this can be a royal pain. You can reduce this pain if, from the beginning, you set up a color control layer.
[Note: this really only works well if you're working on vector animations with single-color objects.]
First, set up an adjustment layer and add the "Color Color" effect found under "Expression Controls." Do this for as many colors as you want.

I recommend naming the controls for the layers you will be coloring rather than the color itself.
Then, apply the "Fill" effect under "Generate." Here, you can option-click (alt-click on PC) and drag the pick-whip (that little spiral button) to the color control in your color control layer.
Now, when the client comes back to you with the comment "The trees should be purple," you won't be cursing under your breath (as much).