Bay vs chestnut
Inspired by this post
We've all been taught that bay horses have a black mane, a black tail, and black legs, while chestnuts have none of these, and that's how you tell them apart. But some chestnuts (see the link above) have a mane and tail so dark they appear black, and some bays have such a small amount of black on their legs that it can be completely hidden by their white markings. How do you tell these apart? Here are some tips.
Genetics
Chestnut (e/e) is recessive to non-chestnut (E/_), so if you can get your hands on the pedigree and both parents are chestnut, then the horse cannot be anything but chestnut. But if one or both parents are bay or black, it doesn't tell you anything.
Legs
Bay legs: the pastern and fetlock at least are black. In wild bays (right), a touch of black on the hocks and knees is common.
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Chestnut legs: red down to the hoof, frequently with gradual lightening.
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Ears
In bay horses, the rim or at least the tip of the ear is black (and you can see it from the back too).
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Chestnut ears for comparison:
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The untrustworthy mane & tail
Some chestnuts' mane and tail are two different colours. This isn't something I've personally ever seen on a bay. If a horse has a black mane and a brown tail (or vice versa), it's probably a chestnut.
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From what I've observed, the dark chestnut tails tend to be lighter at the base, whereas bay tails tend to be more uniform in colour (not accounting for discolouration due to sun exposure).
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Example
Left: red legs all the way down, red ears. Nevermind the black mane and tail this is a chestnut 100% Right: black pasterns and fetlocks. You can see the black rim on the ears. Wild bay.
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Quiz time
