"Let us walk in the woods, and tell sad stories of dead kings and lost princes." The dry leaves and fallen twigs snapped under her sandals, and the hem of her yellow robes dragged in the dirt. "Let us remember those forgotten, long ago turned to dust, names erased from history." The scent of autumn was in the air, of rot and wet and mold, as the world prepared for it's winter slumber. "Today we shall revel and mourn in our life and in our death."
The farmers followed behind the woman, their workday clothing stained with mud and sweat, out beyond their fields and into the woods that they avoided even looking at. The children of the village huddled together in the temple. Locked behind a barred door, and ordered not to open it before the rising of the sun the next morning. None of the farmers knew when that next morning would arrive, as the sky was without sun, and had been the whole day long.
When she came, as she did every year, she brought them through the center of the village, and out into the woods. No one ever saw her arrive, but they could feel her coming. The could feel her approach. They could feel it in their bones. And so they locked their children away and went with her. Most would return, and some of the women would come back pregnant. Some years a child would be born... different. That child would be taken it's first autumn with the adults into the woods. It was never returned...
Some lands are not suitable for people to live on naturally, but there are ways that that can be changed. Rituals, bargains, magics that can be done. Those in Yellow are members of a fertility cult that serve an ancient genius loci who demands a sacrifice every year. They are the descendants of those who made the original bargain, and carry the divine (demonic?) taint of that bargain.
Image Source: The King In Yellow by Dusk-Abomination