Sometimes you can get a male with two copies of the X (or is it Z in waterfowl?) and get a false female.
What's so wrong about vent sexing? I'm sorry...but you can't go wrong when something literally shouts to you.
I didn't realize Sebs were color sexing. But, vent sexing is one of the best methods to see if it's male or female. It's honestly not that traumatic? They don't "scream" any more than as if you picked them up normally? Once good at it, you can sex in less than 30 seconds?
Feathers Acres, I'm sure you meant your reply as a "calm it". I'm sorry if speaking straight-forward about the anatomical features of waterfowl or other breeding animals made you shirk away.