Well, I'm in Germany...
This is what it looks like..:
http://www.monster-hopups.de/product...oducts_id=7560
It says RPM in that shop, but it's not.. I buy it(cheaper) at a craft shop...
I think if you do a search here at RCU under like "dying wheels" you'll find the right name.. Maybe it's also "rit" dye in the UK.. Google it.