I need to buy a new bag that will hopefully be as multi-purpose as possible (good for work, hanging out, etc.) I love the color of the slate blue bag but am not sure if the color makes it not as useful as the tan or the black. I love the idea of both the tan and the black bags. The tan one seems more of an all-season bag, whereas the black one doesn't seem as suited for summer. I don't know which to pick! Please help! and.....which color do you like better for this kooba? Thank you!!!!