Colors INSIDE of windows?

[Bill Sconce]

I'm wrestling with one of those "WHERE is this thing documented??" questions.
It's not a big deal, like kernel builds or boot problems, just cosmetic.

How do you choose colors for the insides of windows?

By "insides" I mean default colors for window components used by the apps,
not the window manager's decorations (title bar, min/max buttons, etc).

I suspect that a default is set somewhere, because everything seems to use
the same color (a mild grey, rgb 216/216/216, which although not unpleasant,
on my screens looks like a certain default theme used by a Redmond company).

Examples of the components I'm after:
   o  The "File .. Edit .." bar (e.g., sylpheed, galeon, dillo, mozilla)
   o  scroll bars  (almost every app)
   o  messages (e.g., area at the bottom of galeon/mozilla which says "Done.")

I've done a lot of looking at X documentation, and a lot of googling, and
a lot of probing of xinitrc, Xdefaults files, and so on.  (I may have been
within one file of finding the answer...)

Does anyone know the answer?

TIA -
Bill

Footnote - it's not the Xt switches, -fg / -bg, etc.