Not sure if they would make a soap white or not, but the bentonite clay is more of a gray color. And the clays are more commonly used in shaving soaps for slip.
But also note that benonite clay is best for those with oily skin because they dry out the skin. So if your customer had dry skin they might not be very happy at all.
And kaoline clay is a more white color and is great for those with normal or sensitive skin tones. And is more or less ok for anyone to use.