why not dye the olive oil? and i think it should be a color that is distinguishable from blue and which, if mixed with the green bile, will give a distinct color. blue would give you blue-green which still might leave doubt. red, on the other hand, would mix with the green bile and make brown. if you had brown stones inside, then the lipid content came from the oil you just drank. what is a good non-toxic red fat dye?