all cats carry the tabby gene, even solid colored ones, so a solid cat can pass on tabby stripes to its offspring, depending on the genes of the cat that it breeds with. That's even true of Siamese, whose light coat and some alleles suppress the expression of the tabby gene. Cat coloring and coat patterns are complex, depending on a variety of genes that either enhance colors and patterns or suppress them, and also on mutations.
It's possible for a genetic line of cats to pass on a recessive gene for many generations without it being visible until the right mating with a cat who also has the recessive gene and the right combination of other genes for the trait to be "expressed" or visible.
But the colorpoint markings of Siamese are due to a mutation that is not commonly shared by most cats like the tabby gene is. So if kittens have colorpoint markings like Carys' siblings, it's likely that there is a Siamese in their recent ancestry, or some breed that derives from Siamese, like a Himalayan (which is fluffy).
If there is - or was - a Siamese, Himalayan, Burmese, etc. among the ferals, its genes and traits could be mixed into the feral colony in more than one cat in the colony. So some of those traits could appear where least expected, like Arthur's big ears, which look Siamese to me. Several of those ferals that you feed, plus others in the colony who don't come to your place, could be related over the generations, swapping ancestral genes back and forth.
The colorpoint markings were so noticeable in the siblings of Carys that they could have had a Siamese father and (Scooter?) might carry some unexpressed Siamese genes that matched up with the father to produce Carys' colorpoint siblings. Carys might have a different father than her litter mates.
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