Yang,
The 2 times that I raced at TX state champs @ Mikes I ran Purple/Grey then Magenta/Magenta. I think this was due to the change in the brand of carpet used. CRC for the Magenta/Magenta...With the new breed of tires, I'd probably run Lilac/Yellow.
At Hobby Town SA I always ran Pink/double pink, except in 2005 we all ran pink/purple with .018 front springs. Now we all use .020s hence the softer DP front tire.
Here in Hawaii, I've run Pink/double pink and 2 stage DP all around with good results. I tried DP rears and Magenta rears but my car was loose (traction was low too
). Some guys (BMI) are here are using DP all around and their cars handle good. I think that some cars are better suited for different tires types. I know that when I had my R5, I was always looking for more steering....so you could probably get away with a harder rear tire.
Even with pink rears that is still more firm then the yellows being used in carpet.