Bear in mind, though, that what the program will do between those two keyframes is blend from one state to the other. In other words, if you have your diffuse colour set to white in frame 1, and red in frame 30, then somewhere around frame 15 it will be a nice pinkish tone. If this isn't what you want (and from what you're decsribing, it's not), then what you need to do is set a third keyfram, somewhere between the two extreme states, to show where you want the transition to start. Set this to the same colour as in frame 1. This will then stop the colour of the required bodypart from changing until you want it to appear.

jonthecelt