While I agree with you fully if you take on the comic book releases of Garfield, then yes. he need black stripes. However if taken from the movies perspective, he doesn't have black stripes, and he sorta is the Arogant looking, sluggish cat, with a quick mouth (pun intended) and self-loving persona.
While Garfield is usually seen as the "bored" Cat, he really isn't. His a comic relief, where everything he does is fun, cause he finds all others around him, less inteligent than himself, and thus find most of them boring unless it fulfills his own agenda of getting that delicious food. He is the Lazy cat, that doesn't wanna do things by himself physically, but use others to his entertainment, and move along to the next if he get's bored. Not saying he doesn't have a heart. Cause he clearly has one, and even goes out of his way more than once to make others in his circle happy. Though... he doesn't mind there being a edible reward in the start, middle, three quarters, and end along the way.
But yes, I love this picture, looks great, and amazing, keep up the great work ^^