Stewart is sitting in his office, which is lighted with a bluish neon light, eating a red apple. Even though the apple is bathed in bluish light, he continues to perceive it as red. This illustrates:

A) the trichromatic theory.
B) retinal disparity.
C) the opponent-process theory.
D) color constancy.

Answer: D
Rationale: Perceptual constancy is the ability to perceive objects as having constant shape, size, and color despite changes in perspective. Color constancy allows us to recognize an object's color under varying levels of illumination. For example, a bright red car is recognized as bright red when in the shade or in full sunlight.