What are the constraints on individual picons?

Each final directory in a database may contain one or both of a face.xbm file and a face.xpm/face.gif file set. Picons in all formats are constrained to be 48 by 48 pixels in size. Furthermore, XPM picons are in the version 3 format of XPM and must use only colors in one of two limited subsets of common colors. This restriction minimizes the competition for colormap space for many users and usually allows applications displaying picons to do so with the standard colormap. GIF picons are equivalent to their XPM counterparts with the XPM "none" color converted to "grey75" (rgb:BF/BF/BF) and marked as transparent.