Brown Calyx

to help pick out a previous answer -- most likely just senescence... pistils turn orange-ish and retract until they are little nubs or curl up small etc... As the plant nears end of life (senescence) it will go through some inevitable changes... and this can vary by plant a bit - e.g. canopy may turn a different color. pollination can have the same effect on pistils and slow bud development.. do you have any male or hermie plants in the room? yet to hear of immaculate conception in plants... usually, but not always, happens top-down (parts with potentially too much light/heat speeding process), so maybe look around for nanners but i wouldn't worry too much... should be doing that alreaady, anyway. It's only going to pick up and all over plant. It is one of 3 metrics you should use to determine harvest window -- trichome color, pistil color, bud density.