No, it can't be justified - not with the present testing regime.
http://www.city.ac.uk/avrc/members/j...lour_study.pdf
As pointed out, substantial numbers of people with PERFECT colour vision fail the bull**** tests JAA employ. The key word is RELEVANCE. The FAA employ RELEVANT means testing, and how many accidents involving FAA pilots who would have failed JAA tests are related to colour vision? NONE.