The use of color in Batman: Shadow of the Bat #93 is used as representation for many things throughout the course of this comic. The first real application for the color happens early on in the comic book, constructing the setting. The characters are in a dark factory that is covered in all sorts of desaturated colors and dark imagery which really helps to set the mood for the comic. On this specific page, I think that the illustrators used the heavy contrast of dark to light from the walls to the characters skin and the objects in the room to create a feeling of angst inside the reader.
Another common theme that the illustrators use color for is to represent characters personalities. The fact that Harley Quinn is wearing a jesters outfit would make any layman think she was playful and funny, but the colors on the clothing represent her true personality, which is slightly more hateful and murderous. They also do this on the Jokers clothing, using the slightly irrational color scheme of purple, green, and orange, on something typically depicted as relatively plain or at least similarly colored such as the suit to depict the irrationality of the Joker’s personality. They even do this on the unnamed captive in the background, depicting him with slightly less colorful clothes to make him look more drab and boring compared to the main characters even before you notice the gag in his mouth.