Blue rears with any of the following fronts:
- Blue
- Magenta
- Pink

Green rears will work with the same fronts and offer a little more steering, but I think most are still using Blue rears. They feel a little more consistent over the course of the run, I think.

I hate pink fronts, but I know some people love them, so I included them in my list

Some people still run the classic magenta/pink compounds (sounds like they are still popular in the UK), but I believe nearly every car at Worlds was using either Green or Blue rears (or an equivalent from a different manufacturer, such as the Yokomo CRT-S compounds.)