All the colors of your bowl, vessel, or mill are the natural colors of the woods used. There are no paints, dyes, stains, or other colors added to the wood. That said, almost all wood species change color and darken over time with exposure to light and air. Usually the changes happen slowly and are too subtle to notice. Some wood species change more noticeably, and I take advantage of that to enhance contrast over time (months and months, typically). For example, Cherry and Mahogany tend to redden, Goncalo Alves gets more orange, and Maple tends to yellow.
In general, it’s best not to display your bowl, vessel, or mill in direct sunlight (unless all UV wavelengths are blocked) if you can avoid it.
All products are finished with multiple coats of Tung Oil–hand-rubbed. Tung Oil is a non-toxic finish. While it is food safe, unless otherwise indicated, I recommend NOT allowing any moisture or liquids of any kind to come in contact with the surface of the bowl or vessel, including fresh fruit. If you do, you run the risk of staining the wood irreparably, and possibly creating a warp or crack. You can use a mill with damp hands without damaging the surface. And you can clean any bowl, vessel, or mill with a damp cloth and dry immediately without risk.