This seems like an easy question that has been asked a lot, but I'm not sure how to phrase it to come up with useful search results. The results I was getting seemed totally irrelevant.
I have a PNG file I created in Photoshop CS5 that is supposed to butt against a colored DIV field on my website. The colors in the PNG file aren't maintaining the exact color information once displayed in Firefox. It was different enough to be visibly noticeable, so I downloaded a color plugin for Firefox to verify. (Oddly, to me anyway, the color actually seems okay in IE.)
The page is coded with #EC8012 and the image was created with #EC8012, but when viewed it's displaying as #E7812A. I verified that the PNG was actually what I created it as by tossing it back in PS.
It seems like a color profile issue, but I don't know enough about them to know what the answer is exactly. I tried saving as sRGB, which is usually what cured similar issues with JPGs.
The curved bit is the graphic, the straight bit under the "T" is the colored DIV field. Both should be #EC8012.