why are most dogs noses black?

Hello jaredsanders and thank you for your question.

Put simply, dogs generally have black noses to protect them from sunburn.

From the New Scientist:

"Why are dogs' noses black? 

While a majority of dogs have black noses, not all do. The noses of
dogs such as vizslas and weimaraners match their coat colours - red
and silver, respectively - and it is not unusual for puppies of any
breed to start out with pink noses that then darken as the animal
matures. I had a Shetland sheepdog that retained pink on the insides
of her nostrils for the whole of her life.

Dogs have most likely developed black noses as a protection against
sunburn. While the rest of the dog's body is protected by fur,
light-coloured noses are exposed to the full force of the sun's rays.
Pink-nosed dogs, hairless breeds and dogs with very thin hair on their
ears need to be protected with sunscreen when they go out of doors,
just as humans sometimes do, or they risk the same ..."
http://www.newscientist.com/backpage.ns?id=mg18825292.900

also see:

"Nose pigmentation is important to protect the dog from sunburn and
skin cancer. It's also quite useful in identifying a dog's actual
color. Genetically black dogs have black noses and genetically red
dogs have liver noses. A black nose on a reddish dog is a red flag
that the "red" isn't really red. It may be a yellow or a sable
instead. The more pigment a dog has on his nose leather the better UV
protection he gets. Pink noses can be spritzed with sunscreen before
an outing, but it's better in the long run to breed away from
unpigmented noses. Pink spots on noses tend to increase in coverage
with active breeding toward maximum allowable white markings. Dogs
with minimal to no white markings seldom have unpigmented noses."
http://www.ashgi.org/color/Aussie_noses.html

Thank you for your question, and if you need any clarification of my
answer, do not hesitate to ask before rating my answer.

Very best regards,

THX1138

Search strategy included:
dogs noses black sunburn
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Perfect. Thanks.  Simple answer to a simple question.