When I create a new image, fill it with a single color, and save it as *.png or *.jpeg, it gets a slightly wrong color. When I save it as *.gif, the color is correct.

Does this have something to do with a color profile? How can I turn it off?

(Gimp 2.6.7 on Mac)

_{BTW, when I use "Digital Color Meter" to check the color in the GIMP window, I also get a wrong value - but that value is again a little bit different.}