Actually what you're talking about is something done since 1992. HP and I think Canon both make prtable printers. HP call's their's mobile printers. Cheapest HP I see is $200. I have an old version of it (
http://h10010.www1.hp.com/wwpc/us/en...51-236267.html ) here, and the quality is decent. The speed is not nearly as fast as a desktop, but it's very lightweight and small (aout the size of a larger rectangular CD case). As for color quality I couldn't tell you, since my version is the 1992 one I was talking about, and color was only a pipe dream back then.
I just checked out Canon, and unfortunately, thiers are even more expensive.