A red poster colour area must be neutralised without turning it brown. What should be done?

Correct answer: Add a very small amount of green

The governing concept is controlled complementary mixing. Green is complementary to red, so a very small amount can reduce the red’s saturation and move it toward neutrality. The amount must be added gradually because equal or excessive green can overpower the red and produce a muddy brown or dull mixture. Black lowers value rather than selectively neutralising the hue, while white creates a lighter tint and does not properly cancel the red intensity. Thus A is the best controlled correction.