Is there a short cut key/command to repeat the last action?

It does not exist to my knowledge. You can post feedback to Apple using the menu item "Numbers > Provide Numbers Feedback"

I would not hold your breath for this feature, though.

no. and I haven't. October 2015. *sigh* as much as i'm now used to dragging a color to a cell, I still miss the repeat last action. I also had a custom keyboard thingy set up in excel to autofill the cell with current color selected. still miss that. but, the standard selection of colors are generous and much nicer.