Sorry, I don’t think I’m going to be able to help much based on your description of the problem. If you can share complete code and assets to reproduce the problem (e.g. a github repository, a ZIP, or a running demo) someone may be able to help debug what is going on here.
Changing the color of multiple objects is very simple in principle — loop over your materials and update them all! — but perhaps more complicated in practice, because you need to keep track of exactly which changes are made to which materials. How to do that is generally specific to your use case.