maybe it's because my school is The Preppiest Place on Earth (in a Ralph Lauren, country club, seersucker way), but i don't think white bags are a trend, at least not here. sure, there are probably less common in New York or Boston until this summer, but a good white bag is important to have for summer here, always. it's so clean and fresh.
so i say ivory, unless you live in a place where ivory or white is really only a trend.