getPixel() return values

I’m using getPixel() for reading a map from a bitmap but it returns somewhat strange and varying values.
I’m also using the conversion from base-10 to base-16 (toString(16))

Like if I have a area of white #FFFFFF it returns #FEFEFE. This is true for everything with FF value, does AS3 never return FF or could the problem be with pngs?
I do use palette based pngs and check that the image has the right colors.

The real problems start with other colors,
when it finds green (#00FF00), it returns FE00. and with blue just FE