The Proto-Indo-European word *kers-
Word *kers-
Meaning black
See also Linear B: ke-ra-no ‘personal name, black’
Tocharian B: erkent ‘black’
Thracian: kersas ‘black’
Thracian: krisos ‘river name’
Synonyms *swordó-, *kʷr̥snós

Comments
O.Ind. kr̥ṣṇá- “black” = O.Pruss. kirsnan ds., FlN Kirsnappe = O.Bulg. črъnъ,
Russ. čë renъ, Ser.-Cr. cr̂n etc. “black” (*čьrxnъ, *čьrsnъ); without -no-forms Lith. kéršas
“black and white mottled, speckled, *tabby”, kéršė “bunte cow”, kéršis ‘schwarzbunter ox”,
keršulis “Ringeltaube”; karšìs f. “Brassen, lead (fish)”, kiršlỹ s m. “ash”; the intonation from
kéršas paßt but not zum O.Ind.

Other words that might be of interest
*temó- ‘dark’, *dh(o)ngu- ‘dark’, *(hₐ)mauros ‘dark’, *(hₐ)merhₓgʷ- ‘dark’, *tómhₓes- ‘dark’