As long as they're a matte material, I would wear pretty much any black skate pant (oth models excepted, unless you can tuck them into a pair of boots during the day) as leggings under a tunic or even some of my dresses. Also, I'm a fan of just black tights, which can work under dresses as well. If you do that, bring a skirt to change into.
My yoga teacher wears legging-like pants under either baggy denim shorts (not so office appropriate though) or a denim skirt with chunky boots and looks pretty cute.