Hi, I play mostly 2 players, so I'm totally biaised for those answers for 3+ players. So just assume a 2 player game.
1. R and RP . then I can use RP as P in this turn.
2.RP and RPG then I can use RPG as G in this turn.
Fully logical, so I agree
3.RP and RG then I can use RP as P and RG as G in this turn
This one is more tricky. You can either do that, which will remove the possibility for you to lock red.
Or you can use them normally. That means the RP hint will be 33% red and 67% purple. And the RG will be 33% red and 67% green.
If you assume you are less likely to use them as a red hint (which I agree), the difference of these % will be more marked. Until you reach 0%/100% depending of how much you use them for red
4.RP and RGB then I can use RP as P in this turn.
Uh. That's even worst. And I really don't like to assume only that. If you want to play 'conventionnally with random colors', just put P as RP and R as RGB.
But personnally, I'm just ignoring RGB. That means RP is 50% red and 50% purple, and so RGB is 50% blue and 50% green.
I put more and more value on trying to reach that:
You lock d3+e3 with a blue/green hint.
I saw a blue. I will put that blue in e2, which will be 50% (or 67%) correct. On the other case, first, your teammate know it's a blue/green card. And secondly, once (you see three blue or three green) OR ((if your teammate put a third blue/green there) and (you see two blue or two green)) you will know the color, and so know if that tile is good or not.
1?. RG and RPG and RPB . then I can use RG as G and RPG as P and RPB as B?
Bad exemple. RG and RPG make RPG be exactly purple. Which mean you have RG and RB left, and so you are in case 3.