What colour appears when equal intensities of red and green light are combined on a screen?

Correct answer: Yellow

The governing concept is additive colour mixing in emitted light. A screen uses red, green and blue light sources; when red and green light are emitted at equal intensities, their wavelengths stimulate the eye together and are perceived as yellow. Orange would require a different balance, blue comes from the blue channel, and black represents little or no emitted light. This rule applies to light, not to mixing physical pigments.