I addressed the history of the white wedding dress here about 9 months ago, which answers part of the question. I also have links to textual sources in this post.

It's hard to pinpoint, because white (even if just in the ground of a colorfully brocaded fabric) was a part of the ideal wedding dress from at least the 18th century, as seen in art and fiction - though it was generally an off-white. Most extant dresses with wedding provenance from the late 18th century through the 1840s are in fact white; because these still exist, yes, these are the remains of well-to-do and wealthy weddings. In the middle of the century through the 1880s, white seems to have become less important, with many extant wedding gowns of the period made in fashionable colors. (They were not just fine dresses one happened to have on hand, but made for the purpose, just like the white ones.) The balance flips back from the 1890s forward, with not wearing white becoming exceptional - something you do if you're having a quieter wedding (for which it was recommended that the bride wear the good suit she planned to travel to her honeymoon in) or perhaps are an older bride. But there's no evidence I'm aware of from this time that it was actually frowned on not to wear white.