Did the colorist do this? Is the newspaper version messed up too? Somebody fouled today's on-line Sunday Garfield, probably when they did that ugly purple gradient effect in the background. Garfield and Jon are covered with little dots. Even Jim Davis' signature is illegible!
As for the strip itself... I generally like when Garfield breaks the fourth wall (it does this subtly in almost daily - see row 3, panel 1), or gets meta-strippy. Garfield is such a self-absorbed character anyway, it feels natural that it would lead to self-awareness about his reality.
I can usually tell what Jim Davis intends as the joke, and what I am inferring from having read too many Garfields, but today I'm a little stumped. I so want the joke to be that Garfield has spent so long acting like a human being that when reminded that he should act like a cat, he is totally unable to comply. Garfield tries to act like a cat and say "meow" but can't do it, feels shame, and acts with violence.
Also Arbuckle does a great slow burn today, and his frozen-handed pose in the last panel is even funnier than the food bowl smashed into his bug eyes.
The title panel gag shows Garfield picking out his costume for the madrigal dinner, finally deciding to be a jester with a big "D" on his hat. The gag makes no sense, but then they usually do not. Besides, according to some Pez dispensers I have, Garfield most likes to wear a baseball cap or aviator goggles.