As you have found out, white is the most diffucult color. In plumbing fixtures, faucets, accessories, etc. I always advise people that they must purchase everything from the same brand to assure a match. If you are buying a white Amer.Std. sink, you must let them soak you for their own basket strainer, soap dispenser, pull out faucet, etc.
Kohler is a whole different story. Basic Kohler white, in sinks, toilets, etc. is DIFFERENT than any other company. Many tile companies actually manufacture 2 different 4" white tiles, usually 100white, and K101 kohler white.