Tights - what is acceptable?

[Makemeaname]

Just received my first order from snag tights and they're so comfy but I've realised I have no idea how to wear tights.

1. I'm probably wearing a red mid-thigh dress to a christmas party next week - have got both 50 and 80 denier blacks, which would be better? Bonus question - ankle boots or ballet pumps, not really a heel person and limited time to go shopping.

2. I bought a pair of their slate (dark grey) 80s, can i wear these with a black dress for work or are black tights better? If not, what sort of colours do these tights work with?

My legs are too awful for sheers so that's not an option but I would love to wear dresses more often.

1. I'd go for 80d if above knee. Just personal preference.
2. Yes

I would wear black tights with a black dress, and the grey tights with the red one, personally. Grey tights will go with almost any colour, but especially green, red, and dark blue. Also, ankle boots are preferable to ballet slippers.