You are right, PZ, Italy has been recommended for mutual recognition by JAA under JAR-FCL 3 (Medical).
As I understand it, the CAA should accept and issue a UK JAA Class 1 on the strength of your Italian JAA Class 1 without further testing.
The CAA eye exam is very thorough and as far as colour vision goes you get three bites of the apple.
1. Ishihara plates, which as you state, you cannot do
2. Beynes Lantern Test
Single coloured light - one at a time - white, green, red, amber, blue. Viewed in a mirror (Total reflected distance approx. 5-6 metres) in a darkened room with a lamp illuminating a patch of wall alongside the mirror. No errors permitted.
3. Holmes-Wright Type A Lantern Test
Pairs of lights - various combinations of white, red and green.
Lit room and again in same mirror. If one error is made (Possibly two) the test can be retaken in a darkened room after a period of light adaptation. No errors permitted in darkened room.
Obviously if you fail all three, you wil get a deviation issued to your CAA issued Cl.1 restricting you to daytime flight only (IFR is permitted) and no public transport, i.e. passenger carrying, flights.
If you have an unrestricted JAA Cl.1 from a mutually recognised state which you can exchange for a CAA issued JAA Cl.1 without further testing, why muddy the waters and take the risk? Just do the straight swap.
Hope this helps,
2close