You can talk to the artist about this and they might be able to provide you with insight pertaining to it staining and being covered. I don't think that it being covered by a shirt is a huge deal as I have a family member who got a tattoo on their chest and it was covered by shirts while healing.

A good artist will talk you through your concerns and explain the best way to handle it. If you are worried about the allergy you can ask them because they can give you more insight and all that.

Talking to the artist also helps you get a bit more comfortable with the person doing the tattoo or that's what I have heard from the family members I have who have gotten tattoos.