I looked into theose 1 year ago. I think there were two generations, one for the '04 Sti and one for 06+, in addition to the blues for WRX.
The later ones were said to be better.
I could probably not dig again where I've read this, was burried somewhere.
There were reds for V7 Sti as well, but the guy that was selling them on ebay.co.uk refused to answer my questions so I passed.