OK, I am lost now, but I work every day alongside television vision engineers shooting HD productions and they colour balance by looking at the Grade 1 monitor in front of them by judging what they see with their eyes. There is no measuring other than by the brain! We are not talking about graphic design, we are talking about maybe 5 highly trained engineers controlling 20 cameras by each looking at a monitor that is lined up identically to their colleagues' monitors. I find it hard to believe that you can achieve this with any level of color blindness which is probably why the BBC put every one of us through a colour blindness test before employing us. Yes there are different levels of blindness, but if your particular strand mixes purples and blues, it would be difficult to correct a blue tint in the blacks if it could actually be purple. Surely?