A method of correcting colour errors which are fundamental in any three primary colour additive reproducing system, by electrically changing the R, G, and B signals with a matrix or masking amplifier which mixes (usually subtracts) the signals in a very precise predetermined amount. The form is generally as follows: R out = R in + a(G-R) + b(R-B) a, b, c, d, e, and f are G out = G in + c(G-R) + d(B-G) referred to as the masking B out = B in + e(R-B) + f(B-G) or correction coefficients