I'm getting this same error:
10:39:06 Skinner: Error running ItemSocketingUI Interface\AddOns\Skinner\UIElements2.lua:805: attempt to index local 'color' (a nil value)
When I open the gemming window. It appears unskinned and can't see what color the gem socket is.
for i = 1, MAX_NUM_SOCKETS do
for i = 1, GetNumSockets() do
for some reason MAX_NUM_SOCKETS returns more sockets than the item has which causes it to loop and try to get info on gems that dont exist :P