Alaskan Red King Crab: this is the highest quality king crab, known for its scarlet red coloring, and rich flavor. Alaskan Reds like to stay in shallower waters and can handle slightly warmer water temperatures.
Alaskan Blue King Crab: these crab like colder, deeper waters, and while they are blue when caught, they turn brownish red when cooked, and are often labelled "Red King Crab" in the stores, even though they are not true Red King Crab. Their legs aren't as thick as Red King Crab, and don't have as rich of a flavor profile.
Alaskan Gold King Crab (aka Alaskan Brown King Crab): these crab are golden orange in color (which make them hard to distinguish from true red king crab) and have much thinner legs than the Red and Blue King Crabs. They have a very mild flavor, and the lowest percentage of meat fill inside of the legs.
Russian King Crab: Shockingly, 75% of the king crab sold in the U.S. is imported from Russia, where the crabs are caught using unsustainable fishing practices, and much of the meat is mislabeled and brought into the U.S. illegally, according to a recent study by the World Wildlife Fund. Be sure to know your sources when purchasing!