Cameron, that sure is a beauty! That bloom color change happened some number of years ago on a pink variety growing at our old house; a few of the flowers were almost totally white while others were the normal pink and others were partially pink and white. I read that cool, cloudy weather could cause flower color to change but I hesitated to believe that was the reason with my tree because I'm in Florida where it's hot and humid during the summer; and although summer is our rainy season and we were having a lot of rain and clouds ... it definitely wasn't cool!
By the way, that's a pretty one you've got there! If you can't find an exact ID you could upload your photos to the general entry in the databse:
Crepe Myrtles (Lagerstroemia)
