Spicing up plain black clothes

I guess black head-to-toe is my go-to outfit, just as jeans-and-a-tee is for most people. When I'm in a hurry, or just simply not inspired in the least to put together a decent outfit (this doesn't happen that often, but it does) I pull on my black jeans (I don't have trousers in any other colour) and put on a black T-shirt. Usually by noon I regret I didn't put more thought into my outfit, but if even my black garments were more varied, perhaps it would never turn out boring. (And no hurry should prevent you from accessorizing.)
So here are three small DIYs (and an extra) which I did recently.