Tattoo etiquette - touch up appointments!

Had an awesome tattoo done about 2 months ago. By an artist I’ve been to before. The tattoo healed wonderfully & I love it.

I had a lot of black done and it is clear that there are some areas that are much lighter. I have a touch up scheduled but I’m curious, is there usually additional fees at touch up appointments? I’ve never had to go back before.

The artist didn’t mention a fee but I also do want to assume. Should I just ask?

I want to know tattoo etiquette!