this pack turns all cats with the name kirby into kirby from the Nintendo game series by giving it an custom model and texture, and as it is a cat, you can dye it any colour you like, as you can dye the cats collar which you can use anywhere on the texture. As it is a texture pack not an addon, it should work on any server or realm!
once you have activated the pack, simply rename the cat to kirby with an nametag and an anvil as shown here, and then place the nmetag onto a tamed cat, and it will turn into kirby, this works in the same way that calling a mob jeb_ or dinnerbone works.
now you have your kirby, you can use dye to make him any colour you like, as shown below:
light grey kirby
light blue kirby
pink kirby (the original)