I had this same issue a few days ago...
You have a few options:
There is a color history in the "Standard Colors Dialog" - This is the
window that pops up when you click the foreground/background in the
toolbox. It's the boxes in the lower right corner... If you don't have
the fg/bg enabled in the toolbox you can get to it by File > Preferences
> Toolbox > Show Foreground/Background...
You could: Use the foreground/background as storage areas, but your
limited to only two colors...
You could: Create a palette to use temporarily, and store your colors
You could: Create a temporary "color storage layer", and paint small
areas that you could pick from with the eye dropper...
It would be nice if the color history was quicker to use... I submitted
an idea/request here: http://bugzilla.gnome.org/show_bug.cgi?id=383083
but it ended up being a solution that wasn't in-line with the way the
developers are moving... Maybe someone else can offer some other
suggestions to improve this functionality...
Gimp-user mailing list