I like to run multiple xterms with a bash session in each (who doesn't?) Usually these are color-coded, e.g. -bg "#880000" for VNC sessions, a dark violet for python programming experiments, etc. These are run from a script or desktop menu, and always the same dozen colors. I create and destroy these xterms all the time. No problem so far.

I rely heavily on the up arrow key to recall past commands. But eash bash session will recall the history of some random previous bash session. What i would like: If i create a new dark violet xterm, the bash shell running in that should recall the history from the previous time i ran bash in a dark violet xterm. Meanwhile, a brown xterm's bash will recall the history of the previous time i ran bash in a brown xterm.

If there wasn't one, is okay to come up blank. If there are multiple past xterms of a certain color, i don't care if it gets confused. This is all for a convenience, not life or death.

Is this possible with some wickedly clever PS1 or .bashrc incantation, or some X windows hocus pocus? Perhaps a different xterm (i actually use rxvt) or something?

I think what you want to do is to use separate history files for each of the different kind of sessions that you launch. I don't know how to set this up exactly, but I do know that it's the HISTFILE shell variable that determines the location of the history your shell uses. You can probably add it to the scripts you use to launch the sessions.

There are also some other HIST* options available for making the command history more sane, such as having it ignore duplicate entries. Check the bash man page.

Add this to your .bashrc file: