This comes from weddingchannel.com:
"Wearing black: the long standing tradition of ladies not wearing black to a wedding has been overturned. Today, even the bridesmaids might be outfitted in black. Just make sure you don't look like you're attending a funeral. Consider accessorizing that little black dress with a brightly colored scarf or blazer.
Wearing white: since the popularization of the white wedding dress in the mid-19th century, women have avoided wearing white to a wedding, so that the bride might uniquely shine in her white wedding gown. While this rule, like the "no black dresses" rule, has since been rejected, a female guest should select carefully if she opts to wear white. Be careful to not select anything that might cause anyone to mistake you for the bride. Since current bridal fashions are sleeker than ever, and many older and second time brides dress in wedding suits, you might embarrass yourself (and the bride) in a white outfit. If you plan to wear white, choose carefully, and accessorize with color."
So many of the old notions of wedding etiquette have fallen by the wayside these days. These niggling worries and distractions are what led my DH and me to have a very small civil ceremony in regular clothes and be done with it!
