Hmmm....that's weird after all the years of it being okay. I have heard of irises changing color like that. It's happened to me with a different iris, but it changed the second year it grew. Did you buy it from a reputable grower? Is that the first blossom from it you've had this year?

Thanks for responding, Catherine. I did buy from a reputable dealer, locally.

For clarification, it's done this for the past 5-7 years, but the last few seasons I was diligent about tagging the ones with the pinkish blooms and removing them in the fall. The dark, velvety purple blooms (that are certainly Black Gamecock) don't appear until late May. I almost feel like it's reverting back to it's parentage or something. I'm not skilled enough to know what might be happening.

LA Irises are well known to reseed easily..and offspring would be a wildcard.