If violet made from red and blue is not clean which contamination should be checked?

Correct answer: Yellow

Violet is a secondary colour formed by mixing red and blue. Yellow lies opposite violet on the traditional colour wheel, so it is violet’s complementary colour. Even a small amount of yellow contamination can neutralise the mixture and make it dull, greyish, or muddy instead of clear violet. Black would mainly darken it, white would lighten it, and green is not the relevant opposite colour in this relationship. Therefore, option A is correct.