Yes, tuxedos are black, and you'll almost certainly see an abundance of dark sport coats at any union, but black is traditionally a no-go color at weddings -- especially for women.
Black dresses connote mourning and death for many people, but there's a difference between showing up to your best friend's nuptials in funeral garb and wearing a sleek, little black number to an evening wedding. As long as the dress feels fun and light, regardless of how dark it is, you should be fine. Sequins usually work, as do black cocktail dresses for formal ceremonies. However, if there's even the slightest chance it could fit into a procession for the deceased, put it back on the rack and slip into something more colorful.