Which controlled addition is useful for making brown appear more golden?

Correct answer: Yellow or yellow-orange

The governing concept is modifying hue and temperature through controlled colour mixing. Yellow or yellow-orange is a warm neighbouring influence that can shift brown toward a golden appearance while preserving its earthy base. Only a small amount should be added, because too much may raise the value or make the mixture strongly yellow. Blue and violet cool and neutralise brown, while green can push it toward an olive or dull direction. Therefore option A is the most suitable addition.