a friend of mine got a black and gray tattoo about a month ago. When he first got it, the lines and shading looked really dark and stood out. He took very good care during the healing process. After about two weeks when I saw it, it wasn't as dark.I'm not saying it's really faded, it just seems somewhat lighter. Is this normal? How much fading should there be?

It can be normal.

Different skin types accept / reject various inks colours and ink brands in different ways.

Talk to the artist about touchups.

Not tattoo will look as bright as it does the first day. They will all fade somewhat, some more noticably than others.

black and grey always looks super dark when its first done... and in my opinion the redness of the skin after getting a tattoo almost makes it look even better.

they lighten up a little, but not too much.. it should stay the way it is now for a long time. black and grey holds up nice.