Where does “чёрно-бурый” come from?

чёрно-бурый (Russian) comes from Russian чёрный, from Proto-Slavic čьrnъ, from Proto-Balto-Slavic kiršnas, from Proto-Indo-European kr̥snós, from Proto-Indo-European kers- — black, dirty; run; to run.

чёрно-бурый (Russian): black-brown

Definitions

black-brown

Ancestry of “чёрно-бурый”, step by step

чёрно-бурый traces back through two separate lines of ancestry.

via Russian чёрный

Step	Language	Word	Meaning
1	Russian	чёрный	black; rough, coarse; back
2	Proto-Slavic	čьrnъ	black
3	Proto-Balto-Slavic	kiršnas	black
4	Proto-Indo-European	kr̥snós	black; dark, dusky
5	Proto-Indo-European	kers-	black, dirty; run; to run

via Russian бу́рый

Step	Language	Word	Meaning
1	Russian	бу́рый	brown
2	Proto-Turkic	boŕ	grey
3	Iranian	bor	—

Every word from Proto-Indo-European kers- →Every word from Proto-Indo-European kr̥snós →Every word from Proto-Balto-Slavic kiršnas →