Topic title should have an 'imo' at the end.
From certain angles, these two heroes can be difficult to discern from each other. They both have somewhat similar models and have very similar colour pallets. In a game like Dota2, it is obvious why it is vital to immediately differentiate between two heroes.
Don't get me wrong, I love Luna's model, and I KNOW there are differences between the two models (black panther, white tiger, etc). But in teamfights with all the particle effects going on, these two can easily be mistaken for each other when just glanced at. No other two heroes are this similar, and that's a good thing.
I'm wondering whether it should be as simple as a colour change would improve this, but I'm no expert so I'll leave it up to Valve to figure out