png files loosing color depth

Hey - I'm using PHP 4.0.4pl1 w/ Apache 1.3.14 on Solaris 2.6. PHP was compiled with GD (1.8.3), jpeg (6b), png (1.0.8), and freetype (1.3.1) I'm trying to overlay text on a existing png graphic, which works, but the color depth seems to be getting reduced. Page info in Netscape shows that the button is a 16bit "TrueColor" image, but the resulting image is much lower in visual colordepth (if not actual color depth). Check out.. http://www.umich.edu/~liamr/button.png vs http://www.umich.edu/~liamr/blue.png (the png it uses to generate that file) Any ideas on why it does this or how to fix it? Liam