I don't know a lot about the wishes. And like I said, I haven't exactly seen enough colour combinations to have a good theory. That one mint didn't particularly seem like a sea-green person or anything.

I don't really know what complexity or size mean other than the obvious. Well, I guess "the obvious" isn't necessarily all that obvious. Bigger-and-more-complicated wishes are wishes that accomplish more things, or more of a thing. If I'd wanted to, I don't know, fix a broken arm as well as my clicky jaw, that might have taken a coin with one more side. Or even a broken arm instead of my clicky jaw. But I don't have any more than the vaguest possible sense of how the size of a wish actually relates to the number of sides it needs. For that matter, I don't know how many sides a coin can have. Maybe it stops at five, or maybe it keeps going up indefinitely and the most powerful coins just look like circles.