What is useful for balancing a watercolour skin tone that becomes too orange?

Correct answer: A tiny amount of blue

Blue is opposite orange on the colour wheel, so it acts as the complementary colour that can neutralise excessive orange. Only a tiny amount should be added to a skin-tone mixture, because too much blue may make it grey, dull, or muddy. Yellow, red, and additional orange would increase the warm orange quality rather than correct it. Therefore, option C is the most suitable controlled adjustment.