Hi!
You cannot vent sex buttons as you do with coturnix since buttons do not produce foam. All button quail colors/morphs (except pure white and some tuxedos) are easily feathersexable if you know what to look for since males and females have very different plumages.
I usually look for 3 male characteristics when sexing buttons.
1. Look for red/rusty feathers near the vent. (In silvers these feathers can be more of a pinkish color. Females never have this).
2. Look for blue feathers around the chest. (For silvers you have to rely on step 1 & 3 since silvers don't get blue chestfeathers. Females never have this).
3. Does the bird have a typical male bib on the throat/chin. (If the bird is of the color blueface it might not have a bib even though it is a male. Females can have a bit of a bib too but males usually have a white one with a strong outline).
For pure white buttons you have to rely on behavior or wait for eggs to be able to sex them.
Hope this helps!