even though it shouldnt make any difference to mattes anyway, its worth noting that i have no vfb colour correction applied and my white balance is set to neutral.
If you still need help, please post a tiny cropped part of your PSD (and the original PNG file). Check your Photsohop color settings (and post a screenshot). My guess there is an automatic conversion going on from the color space of the PNG to your working color space when you import the PNG files. Try to set your working color space to sRGB as a test and see if this makes a difference.