Opponent process theory of color vision explains why they saw the image in different colors.
Opponent process theory of color vision is defined as the way the human
visual system processes information about color in an opposite manner. The
color viewed are usually complementary to each other.
The opponent process cells are located in the thalamus and in the example
given, green and yellow were first seen before the complementary color
which are red and blue were seen after a while.
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