I ran into a transparent png calendar icon which I was using fine on one page over a white background that for some reason showing up with a gray background.
My background color was #FFFFFF or 255, 255, 255 and the area around my transparent PNG was showing up as 245, 245, 240.
Since I was using an <asp:ImageButton>, I was able to fix the problem by setting the BackColor="Transparent" attribute.
I'm guessing that this ...