Pngs darker in browser than jpg...WHY!

I am having problems with png files looking darking once in the browser than jpegs. Does anybody know why this happens? I pulled these images into photoshop to zoom in, sample and compare and they are indeed 1 hex digit off from one another, even though they were sliced from the same file.

Could it be a “web color” issue? Does it have anything to do with how i use photoshop/imageready??? Browser? W3C standards?? crop circles?!?

PLEASE HELP, this is making me sick.

EDIT: i just noticed they’re darker in IE6 but not firefox…