"Rudy" is the adjective you are looking for (it could be used to describe a red/ginger coat of an animal or a person's hair: "Ruda dziewczynka ma rudego kota" = "A ginger girl has a ginger cat"). Using "pomarańczowy kot" would sound rather 'clumsy' if you were describing a real animal.
Ginger is a very common adjective to describe a cat in English. Should we by ngfio's comment understand that "pomarańczowy kot" does not describe such a cat but can only refer to a (probably not real) cat that has actually been painted orange?
"rudy" would be better indeed, as ngfio wrote. I guess Garfield is "pomarańczowy", though.
"rudy" (or rather feminine "ruda") is also the word for a redhead.
of course, but it is better to use word "rudy" if you are speaking about cat (also about some other animal or about a color of person's hair). "Pomarańczowy" is better to use, saying about for example a wall, a furniture, a car etc.