What is defined as Tznius Stockings-skin color and Denier #?
Women wearing socks:
According to majority of Poskim, and the ruling of Admur, women and girls are required to cover their legs and feet with socks/stockings when out in public or in the presence of other men. Even those who are lenient to not cover the feet and/or legs, must cover it when in a community that is stringent. It is forbidden for a man to learn Torah or Daven in the presence of woman whose legs are uncovered.
See through socks/stockings:
If a woman is wearing sheer clothing [i.e. see-through] and her flesh is visible through it, it is forbidden to learn and Daven in her presence, just like is the law if she was not covering it at all. [See Q&A for how many denier is defined as valid and not see through]
How many deniers should the stockings be?
It is forbidden to wear transparent stockings that allow the skin to be seen. Therefore, according to the stringent opinion above and the ruling of Admur that the legs must be covered, the stockings must be dense enough cover all the skin and opaque enough to block sight of the legs. In terms of deniers this would match a very high number, such as 70/80, and would not allow skin color stockings. Practically, while some Chassidic communities follow this ruling, the majority of Jewry is accustomed to allow the wearing of even lesser dense stockings that are skin color. The reason for this is because even skin color stockings blur the sight of the actual skin, and this suffices in this regard. The accustomed Rabbinical directive is to wear no less than 40+ deniers. However, some are lenient to wear even up until 20 denier. Seemingly however, this is invalid according to the stringent opinion, and ruling of Admur.
 Admur 75/3; M”A 75/1; Bahag Brachos 3
 See Piskeiy Teshuvos 75 footnote 27
 Based on Admur ibid; Mishneh Halachos 12/5; Az Nidbaru 10/34; Poskim in Piskeiy Teshuvos ibid;
 Piskeiy Teshuvos ibid
 Satmar and other Hungarian Chassidic communities
 See Igros Moshe E.H. 4/100; Halichos Shlomo 2/12 in name of Rav SZ”A
 Igros Moshe ibid “In truth the skin is not really viewable through the stockings and it only seems so due to the camouflage color. The proof is that if the stockings were to be black then in truth it would not even appear to others that they are seeing the skin”; Halichos Shlomo ibid
 Piskeiy Teshuvos ibid