As a recently qualified PPL, already working on the IMC, I've been following this thread with some interest.
Unfortunately I'm colour deficient, suffering from a moderate deuteranomaly, and have failed the lantern tests at Gatwick and therefore been diagnosed CP4.
My understanding is that this only precludes night flying however, and has nothing to do with IFR versus VFR. Both the CPL and IR syllabi both include an element of night flying, and the CAA have already told me that in the case of the CPL that can be done during the day.
I've argued with them that that same precedent should be applied to the iR, and they're wrestling with that right now. In the meantime, I personally know two pilots who have day only restricted IRs.
Am I missing something here?