According to MARRYJim, a white wedding dress symbolizes purity. It is a sign that the bride has never been married and has not ever been intimate with anyone. It is meant to remind people of a christening or new beginning.
White as a wedding dress color became popular in 1840. Before then, brides got married in a variety of colors, including black. In the modern era, brides can choose from "wedding white" dresses, which include colors such as ecru and ivory. For some brides, bright white is the choice for a first wedding, and "wedding white" colors are suitable for second and subsequent marriages.