I've saved images to PNG using FreeImage with BlitzPlus (Screenshot Magic uses it) but I ended up writing my own wrapper using Snartys code as a reference.
What Perturbatio said sounds right to me, it is most likely the image depth that is causing the strange colours. Take a look at the depth conversion function which is called inside the SavePNG function (just prior to saving - I think it's FIQSend?). Also what colour depth is your desktop set at, 16-bit or 32-bit? 16-bit can affect the images colour depth iirc.
If you still can't get it to work, bump this thread and I'll have a play with it here and get back to you.
What Perturbatio said sounds right to me, it is most likely the image depth that is causing the strange colours. Take a look at the depth conversion function which is called inside the SavePNG function (just prior to saving - I think it's FIQSend?). Also what colour depth is your desktop set at, 16-bit or 32-bit? 16-bit can affect the images colour depth iirc.
If you still can't get it to work, bump this thread and I'll have a play with it here and get back to you.