[athenot]

There are certain variety of blue flowers that, when photographed, always come out as pink. Back in the film days (with the delay to process film), it was often the source of a mind trick. "Could've sworn that these flowers were blue…" :)

[ghaff]

It apparently has to do with infrared reflectivity and even has a name: Ageratum effect.

http://photobotanic.com/color-shift-ageratum-affect/

[athenot]

Interesting! I thought it had to do with UV reflectivity. Thanks for the link.