I have a theory for that yellow and it's really quite simple. Women as a rule are much less hairy than men, so being hairless (apart from pubes, underarms and head, where we all have a lot of hair irrespective of gender) is seen as a feminine trait whereas being hairy is seen as a masculine trait.
So women shaving their legs etc is just a way of appearing more feminine and to mark them out from men, and I suppose a man choosing to have a beard or a moustache is doing the same in reverse.
The reason women don't shave their arms is because very few of them need to. Arms tend not to be terribly hairy. The ones who do have excess facial or body/arm hair quite often have hormone imbalances, but as a rule women have much less body hair than men.
If a woman feels her arms are excessively hairy I am sure she would shave/thread/wax those too.
It is acceptable for women to be small and with little muscle definition, but men want to appear tall and broad and strong, and will work on achieving that, whereas most women tend not to want to be very broad or muscular or to look 'big'.
It's the same with baldness - most men can deal with it even if they don't like it, because it is perfectly normal and very common to go bald when you are a man. However, women suffering from major hair loss almost always choose to wear wigs, because baldness of the head is not accepted as a 'normal' female trait.
All anyone is doing is presenting themselves in such a way as to say to the rest of the world 'I am most definitely a very feminine woman' or 'I am most definitely a very masculine man'. Because let's face it, few men fancy butch women and few women fancy effeminate blokes. It's just the way it is.
That is not to say that any woman who doesn't conform slavishly to a beauty regime is going to look butch, but the purpose of the regime is to take away any doubt as to gender, and to accentuate what are seen as classic female physical traits that are attractive to men.