Gel pen ink is permanent. Isn’t it oil based?

I don't know.  I like them but we always had the clients sign in old fashioned dark blue ink (before colored copying machines) so we could tell original from copies.

Jeri (azpaints) said...

My cohorts in crime used to say "here comes Ms Ego with her ink pen" as they marked docs up furiously with sticky notes and pencils.

LOL... 

I've never used a gel pen.

FWIW

I used to like them but for some reason I dont now.  I think its because in the past the tip would dry out.  You should try one...they do tend to write very smoothly 

Do they even make blue ink anymore?

Yes, all colors.  Blue, black, red, green, purple...

Good.

I have blue, red, black and green in my 4-color erasable ball point pen.

FWIW

Red pens are not used in school anymore. They offend people.

Back in the day, We could not use them Because they didn't photocopy well, even with a color printer.