A friend of mine was complaining her snow photos were dark and dreary. She bought a "nice" camera and even in the Auto Program mode she is retouching and brightening all the images. Well, we had some snow today and she reached out again so we had a practical experiment.
First off, when you are using the camera's internal meter, you are registering the light coming off your subject. When I use a hand held meter, I am reading the light falling on the subject. The camera meter wants to make the reflective light value equal a nice 18% grey color. So, anything white will come out grey--if the camera has its way. You could invest in a nice meter or as a quick trick--use the camera meter and then over expose.
The first image is a straight camera Program shot. We recorded the values the camera chose-- F3.2 1/4000, switched the camera to Manual mode, put the camera's values back in--F3.2 1/4000 and then changed the Shutter speed to 1/2000 and took the second shot. We did it again at F3.2 1/1000 of a second for the third shot. By doing this, we told the camera to keep the shutter open longer which will make the image whiter.
So, if you want to control the white's of the snow, bride's dress, cake, beach sand,...take your reading, record it, copy it, and then adjust to your liking.