Hi Johnny
The green is how much wear (full green is fresh tyres.the dots diminish..then full yellow...they diminish...then red ...they diminish and then crash lol)
on the tyres themselves...blue is cold tyres, dark purple slighly warmer...then i think orange and then yellow is hottest.
you want to try and keep your tyre temps generally under 100 deg (the numbers) in most corners but that is not always possible. in the early laps you want to get those blue tyres heated to get grip but after theyre a nice purple colour, you want them to stay like that if possible.
the thing about rf2 is, it teaches you how to drive better - because you have to learn how to drive to suit the tyres. when i started, i could barely last 10 laps at sebring in a corvette without needing a tyre change. i would guess i could do about x 4 that generally speaking.
too much speed, too much steering input for too long will kill them and you wont end up with nice colours. hope that helps