You're not crazy at all! If you like a style, you should stick to it.
Also, moss and black are really different colors (in terms of what they match, dressiness vs casual, etc), so I think you'll get good use out of both.
If you love the style then I don't see anything wrong with having mutliple bags in different colours. It's not like they're Pradas or something crazy expensive. If you love them and know you'll wear them both, then keep them and love them.