Why are tattoos almost always that same blue-gray color?

Thanks for your help. Many have said the original black pigment fades to this blue-gray color. However, the color black could fade only to gray. Black has no blue pigment inherent. And so, there must be some additional explanation. Could it be that some component of human physiology adds to the black ink, thereby transforming it into blue?

Modern tattoos come in every color under the sun, and tend to fade less.

However, for many, many years the only ink that was generally available, non-toxic, and non-allergenic was a deep indigo blue. As that aged, it faded to lighter blue-gray tones.

Well acctually black can fade to blue.When the tattoo get's old,the colors fade.If the color id black,it will fade to gray,then to blue.

Ever consider that the gray only looks bluish because of the color of the skin mixing with it? How do you know the black ink has no blue in it? It has to have some kind of pigments in it...maybe it has some blue in it after all.

uh...what? Black has to have a blue or purple pigment to make it black right? I believe it's the kind of ink that is used though. All of my tattoos are the original colors with the outlines remaining their original purple black color.