Most people with Colour Vision Deficiency (CVD) are unaware of it until they are tested.
The Ishihara Test is the primary test for initial screening for CVD .
The test used is the 24 plate version and the test is done using the first 15 plates, all of which show numbers in amongst the dots.
The manufacturer's pass standard is 13 out of 15, which allows for mis-readings (even colour normal persons can do this). However, our civil aviation authorities know better than the experts, the designer and the manufacturers and deemed that 15 out of 15 shall be the pass mark for Class 2 and Class 1 EASA medical certification.
If you fail (get even one wrong!) the Ishihara Test you will be asked to take the CAD Test (at Gatwick at least), a CAA only non-EASA approved test which involves you identifying rapidly flashing coloured squares in amongst a background of rapidly flashing grey-scale squares. This has two tests, a quick test; pass this and you're OK, fail and you're onto the extended test (particularly unpleasant by all accounts) - pass this and you're OK, fail it and you're limited to Class 2 certification only with VCL - daytime only.
I'm not sure what the alternative tests at the NATS Aeromedical Centre (AeMC) at Southampton are.
The best thing to do is to go to your local optometrist and have them check you before going anywhere near an AeMC.
Now check your PMs.
