So it must be a problem with your images. Most likely the offending images are saved in PNG but in 8-bit format. AFIK for AM you should have 24-bit PNGs.
Just pick one image that is not displaying correctly, open it in a graphic program - like free PAINT.NET (not the MS standard paint) and resave it as PNG. If there is an option - choose 24-bit color. If not, then 24-bit should be default. It should help - if this is the problem.