A whitish colored stool can be caused by the lack of release of bile from the common bile duct. A white or grayish colored stool is something that should be checked out by your doc.
I had this problem about 6 mos. ago. There are some medical conditions which will cause light colored stools, but when I thought about what I had changed in my diet, I found that I had recently started taking that "new " form of fiber on the market. You know the colorless, tasteless new powdered fiber that you can mix into just about anything? Well, I had been taking it 2-3 times a day, and it is white in color. I stopped taking it, and the problem went away in about a day an a half. Check your diet for anything like that, and if you don't find anything, then you should go see a doctor.