Nice color gradient. Very inconspicuous at first, then you realize what it represents, and it becomes very effective.
I don't know why, but my first impulse was to replace it with a little more, uh, psychedelic color scheme.
(I'll assume this quick-and-dirty 'fan art' is OK with you. Not published anywhere else except on this forum.)
Caption contest? I couldn't come up with any LSD-related punchline for Arthur that doesn't make him sound like Mr. T. :)