In the USA for example many of the standards and requirements are geared up to a system that is relevant to that countries operating infrastructure and norms. For example it is comparatively rare for very low hour pilots to be employed as airline First Officers. It may well be that the FAA considers the higher experience base and general operating environment to be sufficient to allow a different level of colour vision deficiences, than that permitted in the UK.
Bealzebub that is the biggest load of BS that I have seen in a long time....yes you are quite right in saying that in the US airlines look for experience and hours in logbook that are much higher (normally) than here in UK HOWEVER that does not mean that Colour vision testing should be so illogically stringent in UK...Colour vision defective pilots in UK would understand having to gain experience and hours to prove competence and ability but that is not an option - why not? 
I think davidd that you are failing to understand what you do not want to understand ? It is hard to understand why a 19,000 hour US pilot (that is around 32 years of full time flying by the way !) would be seeking a UK medical. However the standard is not designed for such an exceptional case. The standard is designed to satisfy the requirement in the relevant jurisdiction. Not so exceptional as you might think given the fact that we live in a global market and aviation is a truly global activity, many high time US pilots work in Europe and take JAR medicals every day of the week FACT !
Bealzebub - Not sure what your situation is or where you are coming from but I don't think you are a CVD pilot and I would wager that you are possibly linked to the naff system that we have (UK Medical Examiner ?)