Note that if you specify colors in RGB, the parameters C1, C2, and C3 should be specified in decimal form. To calculate this, divide the value by 255. Example: rgb(58,110,165) becomes <?php ps_setcolor($ps, "stroke", "rgb", .23, .43, .65, 0.0); ?>
However, since this is PostScript, most if not all files will be destined for printing and colors should be specified in CMYK anyway.