OM-TOM,
The UK CAA will NOT accept any colour vision tests other than their very own, self-sponsored CAD Test, even though the CAD is not approved by EASA.
(This is the same UK CAA that claims it cannot operate outside the requirements of EU Regulation 1178/2011 and its Acceptable Means of Compliance..........mmmm........).
Apart from that, even though the Fletcher CAM may be a replacement for the Homes-Wright, the UK CAA would NOT accept it, simply because it is not on the list, as published in the AMC (see below).
Bad news but try another EASA member state.
AMC1 MED B.075 Colour vision
(a) At revalidation, colour vision should be tested on clinical indication.
(b) The Ishihara test (24 plate version) is considered passed if the first 15 plates, presented in a random order, are identified without error.
(c) Those failing the Ishihara test should be examined either by:
(1) anomaloscopy (Nagel or equivalent). This test is considered passed if the colour match is trichromatic and the matching range is 4 scale units or less; or by
(2) lantern testing with a Spectrolux, Beynes or Holmes-Wright lantern. This test is considered passed if the applicant passes without error a test with accepted lanterns.