I'm having trouble printing PNG images with (supposedly) transparent backgrounds, and I'm hoping one of this blog's readers can help. Here's one of the images from the Software Carpentry course. If I open it with the Windows Photo Printing Wizard (on XP), it shows up as dark blue lines on a faint blue background; when I print it on a black & white printer, it comes out as black lines on a white background. Open it directly in Firefox (also on XP), and it displays as dark blue on white. When I print it from Firefox, though, I get dark gray on near-black---sort of, but not quite, a negative image of what I actually want. If I create a vanilla HTML page:
<img src="http://www.third-bit.com/swc2/lec/img/py02/negative_indices.292x83.png" mce_src="http://www.third-bit.com/swc2/lec/img/py02/negative_indices.292x83.png"/>
and open that in Firefox, I get the same behavior. Open that page in Internet Explorer 6.0.2900, however, and I get dark blue lines on a faint blue background; printing from IE gives me dark lines on a faint gray background. So, what am I doing wrong?