EU Regulation 1178/2011 Annex IV Part MED states:
MED.B.075 Colour vision
(a) Applicants shall be required to demonstrate the ability to perceive readily the colours that are necessary for the safe performance of duties.
The ICAO Colour Perception Standard has been thoroughly examined by Dr Arthur Pape & Prof. Boris Crasinni.
Have a read of this
article that was published in the Journal of the Australasian Society of Aerospace Medicine a few years ago. It's very insightful and is well worth a read.