Oh, and, though this is a bit random, the reason why the BO mostly appear in the winter time has nothing to do with their clothing, but more because of symbolism.
The four seasons represent the four main parts of life:
- Spring: birth
- Summer: living
- Autumn: dying
- Winter: death
These themes appear in literature a lot, as long as you keep an eye out.
The reason why the BO appear during the winter has nothing to do with the story plot.
It's just Gosho's way of tying in the BO with death using symbolism.