gentiles - Is modesty a positive or negative commandment?

Given that:

1. 
   

   There are two types of Mitzvoth (commandments), 'Aseh and Lo Ta'aseh (positive and negative; ie., "Thou Shalt" and "Thou Shalt Not").
   a. Positive commandments, with some exceptions can be enforced with certain types of rabbinic sanctions but no actual punishments, whereas
   b. negative commandments carry with them specific forms of punishments, delineated in the Torah or derived therefrom.

   
   


2. 
   

   There are also at least two types of Tzeni'uth (modesty), related to dress and to action*. Within those there are also forms of modesty relating to
   
   a. how sexually/revealingly one may dress or how sexually provocatively one may act, as well as (and seemingly separate from)
   b. the idea of not drawing too much attention to oneself generally, whether with outlandish clothing (that is not sexually revealing) or with outlandish behavior (that is not sexual in nature).

   
   

Question(s): Are all the laws of Tzeni'uth part of the same Mitzvah (or set of Mitzvoth)? Do they all stem from "Kedoshim Tihyu" ("Be 'holy'")? If it's all part of the same Mitzvah or set of Mitzvoth, is it positive or negative?

Bonus: if the different forms of modesty are all ultimately connected to 'Arayoth (dancing in the street in a neon green jumpsuit may somehow attract a sexual mate), does modesty apply to non-Jews, who, per the Shiv'ah Mitzvoth Bnei Noah (the 7 Noahide Laws), are prohibited from committing many, if not all, of the forms of sexual deviations that Jews are prohibited from committing?

*For purposes of this discussion I am including speech in the category of action.

UPDATE 6/24/11:
Fascinating discussion on the subject of hair covering, which expanded to Negi'ah and other areas of Tzeni'uth, and ultimately devolved into "AHHH, WHY ARE WE EVEN DISCUSSING THIS?? Why not just permit EVERYTHING!?" here: http://www.theyeshivaworld.com/coffeeroom/topic/covering-hair-once-married

Answer

"Modesty" is a broad term, connoting several values; let me try and list them as dos and don'ts.

Don't pray within view of someone exposed

One concept is the prohibition against reciting prayers while someone naked is within view; if I recall correctly, this is tied to the verse (Deuteronomy 23:15) "and no naked/shameful thing shall be seen within you." Hence, one question of modesty is "how covered-up must I be so that people can still pray within view of me?" For instance, Rabbi Moshe Feinstein recommended that synagogues have an opaque, five-foot-tall mechitza; that way if a woman came to synagogue "with uncovered arms and more", those exposed body parts would not be in view from the men's side (assuming the average-height woman), and the men could carry on their prayers. (The women's exposed hair does not pose a problem in most cultures today, according to Rabbi Feinstein.)

Don't stray after your eyes (Numbers 15:39)

Pretty self-explanatory

Married women should cover their hair in public (Numbers 5:18)

There's a debate whether this is a Biblical obligation or a rabbinic one (and hinted by the verse); the verse takes it for granted that a married woman would have her hair covered in public; though the Talmud (Ketubot 72a) says "from here we learn the prohibition of going in public with uncovered hair."

G-d wants us to behave humbly, without the need to grab attention for ourselves (Micah 6:8)

Listed as a positive value; intended for both men and women (and the Talmud seems to focus this one on men); the only place in this whole answer that actually uses a word with the same root as tzniut.

Be "holy" by keeping yourselves far away from arayot (forbidden relations). (Rashi, Leviticus 19:2)

There is also potentially the notion of mutual responsibility, don't make someone else sin, but that gets to the whole mess of "if she wears something flashy and he sins, do we blame her?", so let's not go there.

What about non-Jews?

Job (chapter 31) complains that he's innocent, he didn't look at other married women, not even single women! There's a lot of discussion how exactly to interpret that halachically, but recall that Job is not Jewish. Now we could debate whether he's saying he followed the letter of the law, or he played it safe by staying far away from anything prohibited.

So as far as non-Jews go, my sense is there is an implied value within their prohibition of arayot to take reasonable steps towards a society that values self-control, plus the positive, gender-neutral, Jewishness-neutral value of Micah to walk humbly with G-d. Not sure you can prove chapter-and-verse an exact requirement beyond that. (Though I must note, on the other hand, that prostitution is likely not included in the prohibition of arayot, see Rambam Ishut 1:4).