Black DT spokes are no weaker or stronger than silver.
As has been said above, much more likely down to:
Crap quality build in the first place.
Spokes a poor fit in the hub, in which case get a new hub or rebuild using spoke washers & new spokes.
Or they’re not actually DT spokes in your wheel, but a cheap generic black spoke that you beleive are DT, do they all have the DT logo on the heads?