When painting white objects, it is tempting to just pull out the tube of white paint and go to town. However, when you begin to realize that whites reflect so much around them, mostly, white objects are only white at the highest highlights. You can create really colorful whites using almost any color and it really adds interest into your paintings.
As an example, here are a wedding couple done using an impressionistic color palette (imposing warm and cool tones), but done in a realist style. I reflected the colors of the water and the sky into the garments. The Bride's dress was slightly creamy, while the Groom' suit jacket was much whiter. Enjoy.
http://www.fineportraitsinoil.com/We...oupleSmall.jpg