A mixture became brown while making bright orange in watercolour. What was the likely mistake?

Correct answer: Blue contaminating the mixture

Bright orange is normally produced by mixing red and yellow, so that combination is not the mistake. Blue is opposite orange on the colour wheel; even a small amount can reduce the mixture’s saturation and make it dull, muddy, or brownish. A clean brush and a clean palette prevent unwanted contamination rather than causing it. The most likely error is therefore accidental blue contamination, making option B correct.