Clay colored stools are a sign of you are not producing enough bile. The liver produces bile which stores it in the gallbladder. It is nothing to be concerned with in terms of a severe disease.
Bile production is dependent on choline (a b vitamin), the amino acids taurine and methionine and I am sure there are other nutrients involved. You could try a bit a choline and taurine and see if the problem goes away.
Usually the milk thistle products will assist with this as well. Most of the formulas are similar in that they have milk thistle, dandelion and other herbs.
You could also try ox bile digestive enzymes and see if that helps.