If a brown mixture is redder than desired and its value is already correct what should be done?

Correct answer: Add a very small amount of green

The governing concept is targeted hue correction with a complementary colour. Green is complementary to red, so adding it in a very small amount can neutralise the excess red in the brown. The small quantity helps preserve the already-correct value, although the mixture should be tested gradually. Thus B is correct. White would raise value, black would lower value, and more red would increase the unwanted bias.