It's worth noting that Decker's 16-color palette can be customized via the Patterns Interface.
See also: the PalImport contraption.
On that note, this may be useful, it's a 16 color palette designed for versatility, and in my experience does a decent job with dithering across a variety of photos. It desaturates them but often captures most of the frequency detail.
https://pixeljoint.com/forum/forum_posts.asp?TID=12795
