Two checks under a marked coat
A Paint foal's sex has nothing to do with its famous coat and everything to do with two plain anatomical checks. First, with the mare held close and the foal standing quietly, lift the tail: a filly has two openings beneath it, the anus and below that the vulva, a short slit with a tapering lower tip; a colt has the anus only. Second, run a flat hand along the belly: a colt has a sheath, a distinct fold of skin roughly halfway along his underside where the penis is housed, while a filly's underline is smooth back to the small udder between her hind legs. Pink skin under white markings can make the under-tail area look delicate in a Paint, so read the shapes, not the colours.
Testicles: confirm when present, ignore when absent
The mistake Paint owners share with every other foal owner is treating testicles as the whole test. A colt foal's testicles may be descended before or shortly after birth and easy to feel as two smooth, firm ovals in front of his hind legs — in which case, together with the sheath, the case is closed. But they may equally sit up inside the inguinal canal for a time, beyond any hand, and a young colt checked on such a day gets written down as a filly by anyone relying on that single sign. Let the sheath and the under-tail picture decide, note that testicles were not felt, and recheck over the coming weeks as part of ordinary handling, when they will usually make themselves known.
Patterns, presence, and other false clues
Paint Horses are bred for colour, and colour is exactly what tempts people into folklore — a loud-patterned foal called a colt because he looks showy, a quieter-marked one assumed a filly. Tobiano and overo patterns land on both sexes without preference, and so do the breed's athletic build and willing temperament. Nipples settle nothing because both sexes carry small teats as foals. If you watch the foal pass urine at rest, a stream from the belly supports a colt and one from beneath the tail supports a filly, which is a handy confirmation of a proper check — but the proper check is what goes on the record, not a glimpse across the paddock.
Handling a stock-horse foal for a clean look
Paint foals are generally bred to be handled and sensible, which makes this an easy job done kindly. Keep the mare in the foal's sight and reach, work in a stable or small pen, and rest your hand on the foal's hindquarters before lifting the tail so the movement is expected. Keep the whole inspection to a few calm seconds, then let the foal go back to the mare. If it wriggles through your first attempt, build the touches into a few days of grooming rather than pinning it down; a foal handled calmly underneath now is safer to examine for life, worth more than a same-day answer obtained by force.
Paperwork is why the answer must be right
A Paint foal's sex goes onto registration papers, sale adverts, and insurance from the very start, and the registry record is awkward to correct once issued — another reason to base it on the two real checks and to have the vet confirm at the foal's first examination if anything felt ambiguous. A colt and a filly also part management company early, since a colt left entire with fillies as he matures is a breeding accident waiting for a date. Once certain, file the result with the foal's papers in KinsLe too — at a show office or a new barn, Pet Pass is the fastest way to show this Paint is exactly who you say it is.