The answer to my question about rain lilies didn't help. The rain lilies in all gardens receiving my extra plants ALWAYS GREW AS PINK. Suddenly, I gave a bunch to a friend and they grew white. They weren't pink and then turned white. She never saw any pink. I cannot upload my photo of the white lilies to show you.
Certified GKH Gardening Expert
In that case it is probably a genetic mutation, known as a "sport": https://www.gardeningknowhow.com/garden-how-to/info/plant-sport-mutations.htm
There are some plants that change their flower color according to the pH of the soil they're in. I can't find any reports of this happening with rain lilies, but here's how it works with hydrangeas:
And here is a discussion of other possibilities: