The headers background is #726CAB, the logos is #7D50AC
This may be a bug with your system's png rendering; it's definitely not true for me. What's your browser/platform?
It seems you are correct, even though the two machines I tested this with are both running an up-to-date Archlinux with Firefox - one of them has this bug, the other one doesn't :/
It's probably a problem with our PNG colour encoding, actually. PNG's have colour correction metadata, iirc.
Ah, yeah, actually, looking at it more closely – we have gamma correction and sRGB stuff in that image, which should presumably get stripped.
Hopefully this fixes it.