a majority (but not all) of the IFTC cast is designed with a real life cat phenotype in mind because I am a cat genetics nerd guy, here's some for cats that have been introduced already:
smolderpaw: seal sepia point tortoiseshell w/ low white
antlerstar: cream ticked tabby
thistletail: lilac bicolor
pineclaw: chocolate bicolor
when designing offspring/siblings/parents I sometimes loosely try to follow some genetics rules for fun, BUT it's never going to be a solid indicator of any heritage because I also regularly break those rules so I don't recommend analyzing the characters' genetics to figure out secret relatives. cats having accurate genetics is a fun extra thing that sometimes happens and not a rule
many characters have colors/patterns that are rare to see outside of pedigree cats because I like utilizing the wider range of colors, but none of them are any particular breed (except for potentially some housecat characters)