After discovering that the colors of my cards (for the card game I'm making) were printed darker than they appeared on my screen I wrote a post for The Game Crafter's forums. It turns out that I should have used the same color (RGB/CMYK) profiles that they are using.
After I had installed them I loaded a test image into GIMP and found that the colors that showed up on screen were a lot closer than what had been printed by The Game Crafter.
Which brings up a bit of advice that if you want artwork, that you had created digitally (2D*), to be produced accurately in a physical way (paper, canvas, etc*) you should find out what color profiles they are using so you can get a sense of what the finished product will look like.
*You could create 3D artwork that can be produced in a physical way via 3D printing, but, you often don't need to worry about colors and therefore color profiles aren't needed. That said I know that some places can print a model in color but I don't know if color profiles are needed in that case.