If a red-orange mixture has the correct value but is too muted what should be done to restore its brightness?

Correct answer: Gradually increase the base red-orange colour

The governing concept is chroma or saturation: a mixture looks muted when unwanted neutralising colour has reduced its intensity. Because the value is already correct, the best correction is to add the original red-orange gradually, preferably in small tested amounts. Option B restores the dominant hue and brightness while limiting disruption to value. Black lowers value, blue neutralises further, and much white produces a lighter tint rather than true brightness.