I'm considering my 3rd B-bag purchase (I have an ivory First and a Mogano City) and I think I really like Mastic. I don't get to use my First much because i'm worried it will stain too easily, but Mastic strikes me as a "darker" light color (if you get what I mean) and I'm hoping it's not as vulnerable. So, Mastic owners, does it dirty easily? Would appreciate your opinion. Thanks!