Color is such a difficult topic. Each brand would like to have you buy all their products, so no one makes 'matching' colors. You really have to get actual porcelain chips of all the colors in question and get them side by side. Even then, the lighting makes a difference. Now, on the other hand, since the tub and sink and toilet are separated enough that the eye doesn't necessarily take all three, or even two of the item, at the same time....you probably can be satisfied with some kind of match, but I think you have to see it, in the showroom.
What color do I like?? WHITE!!! Even there, Kohler has to be different, so Kohler white is different than other whites. Fortunately, if you are doing white tiles, the tile companies make two different white tiles, usually called 100 white and 101 Kohler white.