Which primary colour is not used to make green?

In traditional colour theory (subtractive colour mixing, used in painting), the three primary colours are red, yellow, and blue. Green is a secondary colour made by mixing blue and yellow. Therefore, red is the primary colour that is not used to make green.

Blue is mixed with yellow to produce green, so blue is essential. Yellow is the other component needed, so it is also essential. The option stating none of the primaries is excluded is incorrect because red plays no part in mixing green.

Exam tip: remember the three secondary colours and the primaries that produce each one - blue + yellow = green, red + yellow = orange, red + blue = violet. The primary left out is the complement of the secondary colour.