"斗牛用的红布" can be translated into English as "the red cloth used in bullfighting" or more succinctly as "the bullfighting red cloth".
In bullfighting terminology, this red cloth is specifically known as the "muleta" (in Spanish), which is a smaller, red-colored cloth used by the matador in the final stages of the bullfight to maneuver and engage the bull at close range. However, if you're simply referring to the red cloth in a general context without delving into bullfighting jargon, the first two translations provided would be more appropriate.