I am making a campaign woth half dragon ruling the world. They have split up in different kingdoms, one for each dragon. How would Umbral dragon society be
Are you still using base races? A nocturnal society would be a good start.
You actually visit a city ruled by an umbral dragon in one PFS scenario, though I don't know how much background information on the society it gives as I've only played it, not GMed.
It's in
Spoiler:
True Dragons of Absolom
Make the kingdom a darken kingdom, so the PCs can only see if the have Low-Light vision and/or Dark Vision; also throw in shades once in awhile to mess with the PCs.
Darkness covers the entire region, and the society heavily employs undeads (think Geb), that umbral dragons use as livestock
Read about Nidal.