How to Change Part's Colors with Chat Events?

I have a model with various parts that change transparency when a message is chatted. For instance, if the player says -places cup- the cup model shows up. (I used an old chat door script).

Say I want to be able to change the color of multiple UnionOperations within the cup Model with a similar chat event (say /e set:cupsColor:green) and it would change the color of the Unions within the cup Model to green or yellow or whatever the value is. How would I go about doing this? How should I find the children of a model?