I was too busy to respond when this thread was active. But here is my response.
Unlike most laws, tznius is not a set of rules; the spirit is actually what counts. And tznius cannot be broken down to a set of hard and fast rules either.
Are tight clothes tznius? Depends how tight.
Are bright clothes tznius? Depends how bright.
But even more importantly, it depends how bright AND tight.
See what I mean? Tight is a factor, and bright is a factor. The same tightness that is tznius in purple might not be tznius in yellow, and the same yellow might be tznius if looser but not tighter.
There are a million factors that go into it, and most of them cannot be dropped into little binary yes and no checkboxes.
In my opinion, white is less tznius than other colors, when combined with some other factors. I think that often a skirt that is tznius in brown is not tznius in white. But that doesn’t mean that “white skirt=non-tznius.”