The mother of the bride or groom should coordinate their dress according to the overall look of the wedding, especially in regard to the style and color.  It is really important that all of the dresses compliment each other for the wedding pictures.

The mothers' dresses should be somewhat conservative, and not longer or more formal than that of the brides dress.  Usually the mothers wear a neutral color a lighter shade of the bridesmaids' dresses. 

Here are some guidelines for the proper mothers' day and evening attire for the wedding of your son or daughter:

Dressing Guidelines for Mother of the Bride and Mother of the Groom 

• Mothers should not wear white dresses to the wedding!  I have seen several mothers wearing white dresses that closely resembled wedding gowns!  This looked very tacky!  (I've been there, you should see my pictures)! 
• Talk things over with the bride before wearing a black dress.  While black is a standard color for evening wear, it can stir up lots of controversy when it comes to weddings.  In the past, if either mother wore black it meant they did not approve of the wedding!  Today, black is more accepted, but may still cause quite a bit of gossip.  Ask the bride how she feels about black before you purchase a black dress.

For a very formal day or evening wedding:

Mothers should wear floor-length gowns and these gowns should NOT be white!  Wear heels which are appropriate for the dress, but try to select comfortable shoes.  Coordinate your accessories, but do not wear a watch!  For a formal wedding, the mothers should wear corsages or carry small bouquets.    

For a semi-formal day or evening wedding:

Mothers should wear a street-length dress, again, it should NOT be white!  Heels and accessories should coordinate with the dress.  For a semi-formal wedding, the mothers should wear corsages.

For an informal day or evening wedding:

Mothers should wear a suit or nice "Sunday" dress, again, it should NOT be white!  Or, if the formal wedding is being held at the beach, or some other fun or unusual location,  the mothers should dress appropriately.  Heels and accessories should coordinate.  For an informal wedding the mothers should wear corsages.

Whatever type of wedding your son or daughter may have, please check with the bride about her preferences and don't wear white, even though the bride might say it is ok (I speak from experience), dress appropriately, send the bride and groom off to a very happy start, and oh yea, don't forget the tissue.  Enjoy yourself and have fun!