If you want them to look the same across different monitors,
you're going to have a hard time since most monitors aren't accurate in color
display and/or aren't calibrated.
You'll often have slight differences with any image on the web, to my
knowledge.
Regarding the printer, I have no actual experience with that, but I did read
something along the lines of fine-tuning the printer one way or another.
Not sure it's the first way to go, but you also have http://localhost:631/
to fine-tune your printer's color display.
I don't know enough about the color profiles,
but my point is screens (unless it's a hi-fidelity, calibrated one) shouldn't
be trusted.
If it's for online display, and you want to tweak the colors, I believe you
need a good screen.
If it's for print, if you don't have a hi-fi/uncalibrated screen, the best
would be to play with a color chart (Pantone or another), and compare your
printed picture with what you want, and adjust.
