I had tall red astilbes in one area of my garden and over the years have added many varieties of the pink ones. Now the astilbes that were red have bloomed and they are pink. I am stumped. Any takers on a cross pollination?
color changes happen. especially if the one color is a newer variety...
i've had it happen with tulips, too.
My guess would be that the pink is the more dominant color, so it has taken over. Just like the above poster said...it happens with Tulips too. Red is dominant, and if you have red Tulips planted by any other color, eventually they will all be red.