Ir / Imc
As a colour vision defective pilot, at least in the UK, I find that flying VFR in the US my colour vision is much more important in reading charts and spotting beacons than it is in the UK.
Pirateking states that good colour vision is required for an IR. But in my experience flying instruments in the US is that it mattered far less, charts are easier to read, beacons are of less importance etc. Maybe that is why the FAA take a slightly more reasonable view on CVD.
IO540 suggests not doing the ground school in the US and Gertrude suggests that the cost in US does not factor in lost earnings. Both are down to personal circumstances.
I did my PPL and IR in the US and find that the total immersion route is best for me, doing the PPL in 2.5wks and the IR in two weeks from almost zero start. The ground school fills in the gaps as you go along, putting everything into context very easily. Of course any reading you can do is bound to help and if you can get to a level to take the written before you go it is one less stress while you are there. Sportys.com and mywritten.com have good online practice written exams for free.
As for loss of earnings again that is for the individual situation but in my case was effectively zero. Aircraft hire is in any case higher than my hourly rate when I am contracted and so I prefer to extract the maximum value from that by maximising progress and concentrating the learning. May not suit everyone but it works well for me. A further factor might also be the flight test costs $500 inthe US and possibly £700 in the UK. Well that covers the airfare.
As for IR lite - well I think I already have that based upon the fact that I do not have sufficient real world IFR experience to take off into a heavy IFR environment safely and with confidence just as it was for the first few flights after getting my PPL.
Perhaps that is a route to seperate the traffic streams and keep everyone happy with use of controlled airspace and jet airways etc. being based upon experience and currency in IFR. A high level of both being able to open the gates to the other world where presumably both will be at home together. Meanwhile us less fortunate souls still get to pootle around in the murk as needs and experience permit, building confidence and experience but doing so as safely as we able.
I will possibly follow IO540's suggestion and see if I can add the CAA/EASA IR at a later date and with the benefit of some more experience. However I guess that the CVD will prevent that and which will be a shame.