Parker, I'd choose the blue -- and bet most buyers will, too.
There are definitely purple hydrangeas out there -- all varieties of purple. I had a huge hydrangea in the back yard that was purple, on occasion. Nudge your soil toward neutral or slightly acid and, voila! Purple!
White hydrangeas stay white, but you can play 'colors' with most pink and/or blue varieties. I think they're all gorgeous, and butterflies like them, too. :-)