How do I get the gray colored scratches off of our white porcelain sink?

Be careful, very careful not to void your warranty by Kohler. First, try baking soda and water made into a paste and use the scrunge side of a sponge made for use on teflon. That usually works, if the scratches are not through the enameling. If the scratches are still evident, use Barkeeper’s Friend (my product information endorses the use of this product). If the scratches are through the enamel, it is probably still covered under your warranty. Mine was a black porecline over cast iron sink that a housekeeper scratched by using improper cleaning supplies and techniques to treat superficial scratches, voided warranty. A hint, when you are scrubbing pots, pans or metal objects, protect the sink by placing a tea towel, bottom rack (Kohler sells them) to keep it from scratching.