I don't think virginity is anyone's business besides the bride's and the groom's. When I go shopping I might get a colored dress and even if I don't I'll be focusing on the silhouette and design, not the style.
I've never even heard of that. I thought it was just white in general but she can go with egg shell white or something else if its a preference. these days I feel like people just stick with it regardless of those customs. its their wedding.
I don't think it matters, and I don't know many who do think that it matters. I was just wedding dress shopping a couple weeks ago with my sister and she wasn't specifically looking for off-white dresses. She was just looking for what dress was "the one".