My brother in law inherited the family Christmas cactus which always had red flowers. He gave me some “leaves” and my little C cactus is healthy and growing well. It is now flowering with lovely white flowers with pink stamens. ??? Any ideas what happened?
What most likely happened is that you got a "sport", or a genetic mutant that arose on one part of the larger plant. The cutting you planted must have carried the mutation. Here is more about plant sports:
Some Christmas cactus plants do produce white blooms, so now it seems you have one of those: https://extension.psu.edu/plants/master-gardener/counties/adams/news/2012/getting-christmas-cactus-to-bloom