If I were to write such a thing, I'd probably have it as a pallet
option. "History Pallet" let's say whos contents are entirely dynamic
and populated by firstly the last used colours and secondly by known
colours (in case of opening)

Or, since we already have a swatch sub-menu, we could simply add a "History" checkmark option to it, like this (6-frame gif animation):

http://www.opendesignstudio.org/inkscape/samples/ui_changes/history_swatch_activate.gif

This could add a colour swatch to the front (left) side of the colour swatches every time a colour is chosen. That swatch would continue to change colour until the filled object is deselected, which commits that swatch to the stack, like this (3MB):

http://www.opendesignstudio.org/inkscape/samples/ui_changes/history_swatches_sample.avi

Alternatively (or additionally), we could place a little history stopwatch icon beside the fill and stroke colour boxes, and when clicked, it could display a temporary floating swatch history box that disappears when a colour is chosen from it, or something else is clicked. This would have the advantage of keeping a separate history for fill vs stroke, which may be useful as well.

Thoughts?

-C

That way you can sort of say "Well I want this fixed pallet" or "this
history pallet"

Also keeps it away from the fill and stroke which is already a bit
beyond simple in terms of ux.

Martin,