An artist needs a subdued orange for a shadow area. What is the most suitable way to lower its value and intensity?

Correct answer: Add a little blue and a suitable dark colour

The governing concept is the separate control of intensity and value. Blue is complementary to orange, so a small amount reduces its saturation; a suitable dark pigment then lowers the value for a shadow. White would raise the value and create a tint, more yellow would keep the colour bright and warm, and water mainly changes transparency rather than reliably darkening the pigment.