The Blood gang originated in California and they are obsessed with anything that starts with the letter B. Therefore, their main color is Red, and any variation of Red. Their sign is a hand signal that is created by twisting up your fingers on your hands to resemble the letter B.
The Bloods gang color is red, for blood. The gang has a variety of signs, some are singular and derived from the American sign language for the letter B, or more complex signs done with one or both hands.