Why is Safari on my Powerbook screwing with colors?

I’ve designed a background image for my website, which is repeating on the X axis and at the bottom of the image it fades into a solid color which I set as the background for the page, but when I view the site in Safari on any Apple laptop the colors are different, but still have the same Hexadecimal value. I know it looks fine on my iMac, and when I take a screenshot and view it on my iMac it looks fine, what’s going on?