Do what your friend did. Make an appoinment with the CAA medical HQ at Gatwick. Go down and have an eye test. Cost is about £27.
As you know colour blindness is not as black and white as people think (pun intended). Some people may only be very slightly effected whilst other may be quite severe.
I wasn't sure about my colour vision so went and got it checked out with the CAA. Whilst my colour perception isn't perfect it was good enough to pass Class 1 medical with no problems............. and now I fly the mighty C152 !!