black white brown
Horses are different colors because different kinds of horses are naturally different in color. Some horses were also bred to be certain colors.
Some times all it means is your horse is getting older
Morgan horses can come in all solid colors, roan, grey, and dilutes. There are some that have body spots (pinto) markings, but these are rare.
Tennessee Walking Horses can be nearly every color horses naturally are.
Well there are certain colors that horses cannot be, such as blue, green, purple, etc. There are also arguments over some horse colors and their terms, such as Albino. There is no such thing as an albino horse, this term is often used on Cremellos, Perlinos, and white horses. Some say horses can't be white, but they can be, usually they are a maximally expressed Sabino pinto marked horse.
Independently
They are only black. If they have any other colors on them they cannot be registered.
sea horses can change to all of the colors of the rainbow
Some horses do. Zebras evolved to blend in to their environment, probably sun and shade. Prehistoric 3 toed horses merged into their background also. The domestic horses that we have today have thousands of years of selective breeding at the whim of humans. We have bred them with the colors that appeal to us. Left to their own devices they would most likely not have the same coat colors that humans like.
all colors of horses
brown and cream colored
It's hard to say -- but people say horses can only see the colors purple, green, blue, and orange.