Having got a bunch of custom colors defined (thanks to Drew), I need to use them to customize the background color per host. I have named the colors after the hostname, eg
(setq pentacle "#314159") (setq athame "#271828")
so then I tried (at the bottom of the .emacs file)
(set-background-color (nth 0 (split-string (system-name) "\\.")))
but on (for example) pentacle.mydomain.com I get the message in the minibuffer
Undefined color: "pentacle"
I assume I need one or more additional levels of indirection in expanding the system name and splitting off the first token from the FQDN, but I can't see how to do this so that it gets recognized as the variable I defined.