Type A Cartridges only work with eGo-T Type A Atomizers which are cone shaped (tapered or smaller at one end than the other)

Type B Cartridges only work with eGo-T Type B Atomizers which are cylinder shaped (straight walls that create the same sized opening at both ends)

Black Cartridges have an opaque black mouthpiece, but also have a small translucent window that allows you to see how much juice is remaining in the cartridge. 

Smoke Cartridges are a translucent black color that gives a nice finished look to your electronic cigarette, but also still allows you to see through the cartridges so you always know how much e-liquid is remaining.