Final answer:
The afterimage will be red.
Step-by-step explanation:
The afterimage seen by Van after looking at a green computer screen will be the complementary color of green, which is red. This phenomenon can be explained by the opponent process theory of color vision. According to this theory, when the retinal ganglion cells that respond positively to green light are overstimulated and then abruptly decrease their activity, the brain interprets this as a response to their 'opponent' color, which in this case is red. Once the ganglion cells return to their baseline activity state, the afterimage of the complementary color will disappear.