Whoa, whoa, whoa.....I have a lot of blue ink on my body and I've never even been in jail, let alone in prison. You have no idea what you're talking about here. Most people I know with ink have blue ink. It's a toss up between green and blue as to which is the most common outline color.
I never said all blue-ink tats were prison tats. But all prison tats are blue-ink. If you're looking for members of a prison gang, you're looking for blue ink, that's just the way it is.
The designs themselves are the most telling element, obviously. But since this isn't a thread about prison tattoos, and since there are so many designs, I didn't feel the need to go into it.
Sorry you took it wrong. My wife has a blue-ink tattoo herself, and I know she's not affiliated.