I'm making a app which is based heavily on another application that serves a similar purpose. I'm not actually planning on selling it, but I'm wondering whether it would even be legal for me to sell it.

I don't borrow graphics from the other application, but I have a very similar color scheme, virtually the same features (I added a few, but not really significant), and a very similar interface layout. Obviously, I'm not borrowing any code (It's written in Objective-C and mines written in Java).

Again, I'm not actually planning on selling it, I was just wondering in the hypothetical. I'm not sure whether it's just the code that's copyrighted or the actually design itself.