As the result of a total remodel we had a Kohler Bellwether Cast Iron  RH Biscuit Color Three Wall Alcove Soaking Tub installed in our main bathroom last August. Later we noticed a well defined, dingy, dirty looking discoloration on each narrow end of the tub. We were told by four or five professionals that it is "just a shadow" caused by the sloping of the upper part of the tub sides. Nothing can be done and we are stuck with this tub.