After Sharon stares at a patch of saturated green color for a brief period of time, she looks at a white surface and sees a red patch of color. This perceptual phenomenon is best explained by

opponent-process theory

Explanation:

Based on the information provided within the question it can be said that this perceptual phenomenon is best explained by the opponent-process theory. This theory explains that when one color pair is activated it triggers activity from another pair, meaning that the three opposing color pairs ( blue/yellow, red/green, and black/white) are all linked together. Which is why Sharon saw red when looking at a white surface.