From Longman Dictionary of Contemporary Englishprimary colourˌprimary ˈcolour noun [countable] CCone of the three colours red, yellow, and blue, which you can mix together to make any of the other colours
Examples from the Corpus
primary colour• Eight bit-planes per memory bank allows 256 levels of the associated primary colour to be represented.• This type of pattern is usually white with each smaller diamond in the same bright primary colour. 