There is no original cartridge, Colors is free homemade piece of software written by some guy at home ("homebrew") for use on flashcarts, not a commercial game so it is not for sale anywhere. It's the kind of free homemade software that these cartridges are supposed to be used for in the first placeWhere can I find the original?
The developer's homepage was linked in post 2, keep an eye on it because he's still working on Colors so it is often updated:
http://www.collectingsmiles.com/colors/