This cartoon cat looks happy and friendly, so I'd suggest using playful colors like oranges, yellows, and blues for the main body of the cat, and a bright pink for the line around the neck. I would do the left ear in yellow, and the right ear in vibrant blue. Finally, the eyes should be filled in with a bright green to give them a cheerful, mischievous look. The edges of the page can be outlined in black and the remaining area can be colored in white to create a nice contrast with the brightly colored cat.