Answer: No, horses are not colour-blind.
It’s often been a misconception that horses are colour blind but actually, they aren’t what you would call colour blind they just don’t see all the same colours that humans do. They have what you call dichromatic vision meaning they have two colour vision.
What is Dichromatic Vision?
Dichromatic vision is when colours are seen in two wavelength regions of visible light. Horses tend to see shades and variations of blue and green with colours such as red appearing as more green in colour. Humans have trichromic vision meaning three wavelength regions of light and can see all colours of the spectrum.
What Colours Can Horses See?
A horse naturally sees blue, green and variations of these colours, but they do not distinguish red. Even though a horse cannot distinguish red, it can still tell the difference between red and blue. Just because a horse does not distinguish red does not mean it cannot see anything red; a red apple, an orange or a carrot just appears as shades of green or brown to a horse.