Many brides note that their mothers or her future mother-in-laws put more time and energy into choosing their "perfect dresses" than they put into choosing her bridal gown. Perhaps for Mom, the stakes are higher: she wants to look youthful, but not as if she's trying to upstage the bride.
Here are some basic rules of mother of the bride dress to help Mom find the right one for her. ◾Both mothers wear dresses of the same level of formality. In days of fewer fashion choices, this meant dresses of the same length. Today, the mothers need merely look as if they're dressed for the same event.
◾By custom, the mother of the bride chooses her dress first. However, this tradition dates from the time when she also determined how formal the wedding would be. If the bride is making the decisions, both mothers may have enough information to make their separate choices in any order.
◾The mothers do not dress more formally than the bridesmaids.
◾Both mothers should dress so that they do not clash with the wedding color scheme. If the wedding colors are royal blue and silver, the mother of the bride would not wear navy. However, it is up to her whether she wears royal blue, silver, or a coordinating color such as deep rose.
◾Traditionally, the mothers do not wear white/ivory or black. This rule can be waived if the bride wishes.
May your mother wear the same colors as your bridesmaids? There is no "rule" or custom forbidding it. From an aesthetic standpoint, it might look odd to match the mothers to a colored bridesmaids' dress-in ordinary life, we seldom see crowds of women all in hunter green at the same party. But black-and-white is a very common color scheme for dressy women's clothes. If your mother's dress is quite different in style from the bridesmaids' dresses, it is unlikely that anyone will think, "Gee, she's dressed to match the bridesmaids!"
One point never to forget is that it is ultimately your mother's decision what to wear. Some mothers, remembering their excitement over their own weddings, are eager for their daughters' advice. Others have strongly defined tastes and wish to choose their own dresses by themselves. Giving a mother orders is a far worse etiquette faux pas than allowing her to show up in a dress that clashes with the color scheme.