You should definitely wear white gloves with white tie, at least while dancing. One does not want to soil one's partner's dress, nor inadvertently press flesh to flesh! You can take the gloves off for eating.
There are probably different shades and formulations of midnight blue. Mine is blacker than black (it's richer-looking than black which seems to blanch out by comparison) under artificial light, and you can only get a very slight hint of blue in full sunlight. It's a Zegna cloth from the 15 milmil 15 group.
I agree there is variation among "midnight blues", but a truly deep blue would barely be noticeable as not black, even in daylight, unless you were looking for it. I also second white gloves, they really are a requirement. Indoor lighting is now quite varied, with full spectrum incandescents, halogens, and corrected fluorescents. Whatever happened to the dim lighting just to supplement the beauty of candles?