As far as I can tell, you will not get a Class 1 medical. However, the JAR Class 2 (Private Pilot) Visual Standards - Initial Examination says
Colour Vision
You will be tested for normal colour vision with Ishihara Test Plates. If you fail these you can still gain a Class 2 certificate, but it will be limited to flying in JAA airspace, by day only and under Visual Flight Rules (VFR). This limitation can be removed if you pass a colour lantern test, but this can only be done at the CAA Medical Division, Gatwick.
So you can get a PPL, although no IMC/IR. Better than nothing I guess. See more at
http://www.caa.co.uk/srg/med/default.asp?page=538
This will almost certainly be moved to the medical forum, where you'll find a very long Colour Blindness thread....
