Hopefully, they haven't been pollinated. Pistils turning brown early, can be a sign that you have a hermie/male in there somewhere, and has released pollen. Is that a possibility? I hope not, but, 3 weeks is normally too early for the pistils to change color,(except for maybe one here and there) so you better take a close look for balls on your plants.
Thing is its the only plant and i'm 99% sure its total female... The temp gets a lil high sometimes, could this be it?