I think I'm now working on my fourth color change. I'd be interested to see whether others are indecisive about this.
I started out with white/black. It's classic. White hides dirt well in dryer climates and it has to really get oxidized before you can tell. My Smart may live outside for a while; so, white seems like it would be the low-maintenance way to go.
Then I was with blue/silver. My current car is a medium blue metalic. I really like it. I like the Smart blue and I think it looks good with the silver. I've been surprised how the blue I have masks dirt. While Smart's blue is darker, I don't think it will require the washings of a dark colored car.
Silver/silver: I'm going to want the heated seats which means (gulp) a black interior. Although not entirely monochrome, it's close enough to pass. It's relatively understated (for a Smart).
White/Silver. I saw one of these posted somewhere and it looked good, very clean and the tridon silver is less of a sharp contrast than white/black.
Folks have argued for the solid colors because of the color impregnated plastic. I'm less concerned about touching up the metalic paint if each panel would probably cost less than a visit to the body shop.
Yes, I know I can change the panels for $800 (or whatever it is), but I may need more time before confirming.