There is NOTHING to prevent you from doing a JAA IR even with a CP4 colour unsafe medical restriction. This has been done to death on the medical forums. I have an unrestricted class 1 FAA medical by the way...
You do the night rating, all dual. You do the CPL, you do the IR. Yet you still can't fly at night. Fly in zero viz, just not when it's dark. How pathetic. If it was such a big deal, all those FAA ATPL's wouldn't be able to fly 747's in and out of the UK on a daily basis now would they...