I don't think I've ever gotten two batches of hardener that were the same color (from Sys 3). At first I was concerned, but it has never made any detectable difference, even when mixed and matched on the same boat (I'm on boat #7 now with Sys 3 epoxy). I don't pay it any mind now, just a mild curiosity with each box I open. It mixes, kicks, and looks the same on the boat, so personally, i don't think there's a thing to worry about. Sys 3 seems to be really good about QC, and notification if anything slips past them.
Good Luck,and CHEERS!,
Bob