I suppose they are 'colour blind' - as in the red and green - like humans, but they don't see in black and white, as some may believe.
People who are colour blind only have 2 Cones (special light catching cells) and dogs have only 2, as well. With normal sight, you have three.
My dog loves her RED frisbee and that is interesting, because she can always see and find it. Maybe it is because it looks black and stands out - maybe it is her snozzle and her smell sense is so high for locating ... who knows????? Her leash and collar are also red, and she can still retrieve and bring these items, when asked.
I buy this colour for me to see, especially in the sea or in the bush.
I am refusing to look at that damn dress, but I am always interested in anothers other perception.
Like
@jessy_girl posted, I have always wondered if others saw colours differently to me, does that rainbow look different, but then I think about Shapes and Maths etc and wonder where
@Spock is to give an answer to all of this!!!