should you fail any of the further testing after the plates e.g. lantern test then the CAA will offer you a fairly new test called the CAD test at an additional cost(search the medical area of this forum also google and you will get alot more information).
I have a mild colour deficiency which previously prevented me from obtaining a class 1 medical however when the CAD test was introduced last year I immediately sat the test and thankfully passed it, now in possession of an unrestricted class 1 medical.
The CAD test basically measures the degree and severity of your deficency so there is still a chance you could become a pilot. I'd recommend before commencing training that you sit this test.
Any further info then PM me.
Andrew