Water mark on LCW  

A water stain
caused by oil ? Seems odd . . .
I don't know how often it happens, with these chairs -- but I prefer to see the seat and the back made from the same flitch of veneer, so the grain really matches.
At least this one is symmetrical, on both seat and back. For what it's worth, the ideal would be either absolute match and symmetry, or a random grain on both seat and back -- in the same specie, naturally, and with some attention paid to uniformity of grain and color, in either case. This chair almost makes it in the first category.