Which tertiary colour may generally appear relatively light because of yellow's influence?

Correct answer: Yellow-orange

The governing concept is colour value, or relative lightness and darkness. Yellow has high luminosity, so a tertiary colour containing yellow can often appear lighter than mixtures dominated by blue or violet. Yellow-orange combines yellow with orange and is therefore the most suitable choice. Blue-violet, red-violet and blue-green generally appear comparatively deeper, although exact value can vary with pigments and lighting. Option A is correct.