I am sad to say, but I can not draw, I kinda can, but I always hate how my drawings come out, but I still put a lot of thought into this yesterday and this is how I would describe the way Luz and Amity look;

Luz would look the same, but I think that Amity wouldn't keep her hair in a ponytail so she would let it down, but she doesn't like the hassle of long hair so she keeps it the same length. Her green dye had been faded away and she doesn't want it back, but she doesn't mind dying her hair different colors, normally the ends, just depending on however she's feeling on certain days or times.
For her clothes she probably let herself be influenced by Eda and she wouldn't dress all nice and uptight as everyone else seems in their casual wear. She probably wears a plain shirt underneath some kind of jacket that she either stole or Owlbert took it from the human world. She also wears a pair of black (jean-like) ripped pants. I don't mean ripped like purposely in a style type of way, I mean, uneven, random placements, rips and patches.
(I don't think the Boiling Isles actually has jeans.)