Opponent-process cells have been located in the thalamus and the hypothalamus. lens and the retina. retina and the thalamus. cornea and the lens.

Retina and thalamus

Explanation:

According to the opponent-process theory of color vision, the opponent-process cells are present in retina and thalamus. These cells of the retina send the signals of the cells present in the thalamus via a visual pathway.

According to the theory, an opponent-process cell of the retina is designated with a pair of colors to which it responds. The counterparts present in the thalamus detect only the presence of one of two designated colors.

For example, the red/green opponent-process cells of the thalamus can not sense the presence of both red and green color simultaneously.