It's all about receptors in the end.
Humans have three types of receptors in eyes, which help them to see all kinds of colours by combining the Red, Blue, and Green colour.
On the other hand, dogs and cats have only two receptors (blue and yellow) which make them colour blind when compared to a human eye.
From Your Cat To The Butterfly In A Park, Find Out How Differently They See You
Human vs dog/cat
