For the first scenario send the message: If two primary colors end and state the color that results from mixing, <primary color>.

If the other participant sends a primary color in the first round you can end immediately. Given that your partner understands primary colors and mixing you will be done after one round.

The benefit of this solution is that no matter what your partner sends over to you they have the instructions needed to know what you will do on your side, which addresses the coordination challenge.

I think this solution works for some of the other scenarios as well, but I didn't read them all.