Squirrels have dichromatic color vision (cannot tell apart red and green hues).
A 1987 study of the tree squirrel, published in The Journal of Comparative Physiology A, analyzed their colour vision using behavioural tests and examining the kinds of colour-sensing nerve cells in their retinas.
The behavioural tests used lighted panels of different colours. The squirrels learned that when they touched the panel displaying a target colour, a food pellet was released.
The researchers concluded that the familiar grey tree squirrels, Sciurus carolinensis, have dichromatic colour vision. This means squirrels do have colour vision, but they cannot see the difference between the green leaves of summer and the red leaves of fall which means that squirrels are colour blind.