Why are cows black and white? and why not purple and black?

Question

Why are cows black and white? and why not purple and black?

Answer 1

Most mammals have poor color vision - most of what they see is in black, white, or shades of gray.  A cow could be purple with pink spots, but all another cow would see is gray with lighter gray spots.

Answer 2

The pigmentation produced by animals yields the colors white to black.  That is why so many animals are gray, brown or black, or shades.  There are actually 256 colors between white and black.  The more pigment the more color, and darker, less pigment, lighter the color, no pigment is white.

Each species is characterizes by it's own color.  Breeds are also characterized by color.  Some cattle breeds are black and white, some are brown, some are brown and white, some are mixed colors.  Very much like dogs and cats.

Purple is not a natural color in the animal world.  There is no pigment producing pores that make the color purple.  If it occurs in an animal there has to be another reason.  Like diet or environment.