@samblundell
I don't believe there is a cure for colour blindness. I suggest you contact the CAA before progressing with your application so as not to waste your or NATS' time, details below.
Aeromedical Centre
Aviation House
Gatwick Airport South Area
Gatwick
West Sussex RH6 0YR
Telephone: 01293 573700
Medical | Safety Regulation
here is a
link to the standards they require for vision
"An applicant for a European Class 3 medical certificate must have normal colour vision (normal trichromacy).
An initial applicant must make no errors when tested on the first 15 plates of the standard 24 plate Ishihara Test (a series of numbers outlined by different coloured dots, easily seen by someone with normal colour vision)."
Here is a
link for an Ishihara Test