You don't need a Class 1 medical for an IR. You can do a JAA PPL/IR on a CAA Class 2 medical, with the CAA Class 1 audiogram requirements added into it.
For a JAA CPL or ATPL you need a Class 1 medical.
FAA PPL/IR can be done on a FAA Class 3 medical.
I don't get the colour vis requirement with IMC either - one cannot possibly not see the lit-up runway. Also the vast majority of people that fail both Isihara and the Lantern test can see the normal colours they are subjected to in life, and can distinguish the aviation-relevant colours in any practical circumstances.