i have an armband, and i never show it at interviews. just not worth risking having someone judge me based on a bit of ink.
for school interviews (i'm a teacher, just interviewed twice last month, successfully!!) i tend to lean away from overly formal looks. i used to get really dressed up (skirt suits) for interviews, but i starting approaching it from what i'd actually want to wear for a day of teaching, and i feel like it's a more successful approach. i'm more relaxed, i look confident, and thus i seem to do better. i still cringe when i think about an interview i went to a couple years ago in a full out skirt suit. i looked very nice, i'm sure, but i was really warm, and this supposedly super posh school was very casual and relaxed. they wanted me to spend some time in the classroom, but i was so out of place! i couldn't sit on any of the classroom chairs properly, i couldn't crouch down to talk to the kids. it was kind of awful!
colour, comfort, construction, and style.
i tend not to wear black... i want to be remembered (not to say you should wear neon rainbows, but brighter, flattering colour is good)
i don't want to be pulling or adjusting or sweating in my clothes. i'd go with dress pants, the nicest, most comfortable top you have, and the black sweater. the necklace, i'd definitely show a little personality. tasteful, but interesting.