"Not all adult female black widows exhibit the red hourglass on their abdomen-some may have a pair of red spots or have no marking at all; but any markings that are present are bright red. Adult male black widows are a quarter the size of the female, are usually gray or brown rather than black and red, while they may sometimes have an hourglass marking on their abdomen, it is usually yellow or white, not red."[1]
[1] Wikipedia