How can you animate a color change (i.e as a build) in a Keynote presentation? There is no option for color under the Action tab of the build inspector.
One way to do this would be to have two objects that are exactly the same except for the color, in exactly the same position, then have one build out and one build in at the same time, with the effect set to dissolve. Doesn't work quite right.
You could also have two identical slides except for the color change, then set the transition between the slides to dissolve.
Such a disappointing thing that Keynote doesn't support this natively in animations but I mimic color change animation using one of the methods below:
If you can break your animation in 2 slides: Duplicate your slide and remove all animations from the duplicated slide, set the new color of your object in the new slide and set transition on the first slide to either Disolve or Magic Move.
If you cannot break your animation in 2 slides: Copy your object and place it exactly on top of the other (I usually name it with + at the end of the name of the object). Set the built-in animation Disolve or Scale or Big Scale, on the newly created object.