I don't know what product to use specifically, but if you use a translucent powder overtop of your finished product it will look more realistic and won't have the shininess.
I presume that the character you're talking about looks similar to Aang so I'm thinking if you did a thin layer of whatever you end up using it will look best. You should always include a picture of the character you're trying to do in your main post though. More people will be able to help you with color specifications and things like that.
Here's a thread about tattoos
. You might be able to pull some information from it as well.