curious question, do ZSU-57-2 provided with armour piercing round?
if so what color? I assume black?

Apparently so...

"The ZSU-57-2...carries 300 rounds, and the ammunition is stowed as follows: 176 rounds in clips inside the turret, 72 rounds in clips in the hull front, and 52 separate (unclipped) rounds in special compartments under the turret floor. Armour-piercing rounds in clips are placed in the rear part of the turret to the left and right of the guns. Empty shell cases and clips are removed via a conveyor belt through a special port in the turret rear into an external metal wire basket on the back of the turret."

The Complete Guide To Tanks & Armored Fighting Vehicles
George Forty & Jack Livesey