My sister has definitely confirmed he's a boy. I have to trust her judgement, as she's a retired nurse, LOL! Apparently this type of cat is called a "Torbie" -- tortoise-shell tabby
I have talked to my vet today about Skittles and she says that it is maybe easier to win millions in the lottery than to adopt a three-colored boy because they are so rare. So, your sister has won the Jackpot ! Or the boy is a girl !? I remember that mistakes like this can happen. ;-)
Then this little fellow seems to be a very rare tom cat , a calico male maybe. Calicos are not always female but when they are male they have a genetic defect, they are sterile as far as I know.
There's at least three colors. He's a mix of all the kittens in the litter, and there was an orange one, a black one, a white one, and a calico one I think.
I went to my sister's today to meet Skittles. He was the runt of the litter and not expected to survive. He had some sort of neurological problem also that seems to have cleared up. Very much like Ambercat's personality. He probably would've ended up the alpha of the litter despite his size. Very outgoing and not afraid of anything.