Well first off, I'm happy to know there are other teachers on this forum who love MJ bags!! I'm a teacher too!!
i have the flower bag in red, got so many compliments on it!
i say black...metallic bags worry me as the color is prone to wear off.
I didn't fondle it, nor did I sniff it, but it sure was pretty sitting there in the Charlotte, NC Nordstrom store! I see that Zappos.com (free overnight shipping!) has this bag in a couple of colors right now, so, as someone older, I'd advise you to order one from them, then decide if you are in love with it. If not, Zappos will let you return it with no return shipping costs!
I saw the black one at Nordie's and fell in love with it. I think it's a beautiful bag. If you want to be low-profile and classic, I'd go with the black. But if your style is more trendy and fun I'd go with the nickel.
I thought it was a very nice quality bag, btw... nicely made.
And no tax! - That's my "older" advice as well. I've found the MbMJ bags to be very high quality.