I don't think you should say anything, and I think you should let them come to that conclusion themselves. They may be trying really hard during the transition period because they want people to see them as their gender. It may also be the case that they are into fashion and have always wanted to express themselves in this way. These are just some assumptions...but there could be a million different reasonings for their presentation.

Just like cisgender people, you should respect their clothing attire regardless of how well done it may be. If they bring it up you can politely suggest a more 'nature/whatever' look, but don't bring it up unless they do first.