Did you try reexamining everything in all the rooms you've been in? You might've missed something.
I'm pretty sure I did. I noted down all of the names of the paintings because some I couldn't tell if they were grey and I even tried seeing if there were secret spots in the walls that I could walk through that I couldn't see.... Now that I typed that I realize how stupid I was trying to do that in a tower. I did collect three of the pink hair strands though :D