Where does “колечко” come from?

колечко (Russian) comes from Russian -ко́, from Proto-Slavic -ьko.

Ancestry of “колечко”, step by step

Step	Language	Word	Meaning
1	Russian	-ко́	Creates diminutives of normally neuter nouns and adverbs, normally having a colloquial register
2	Proto-Slavic	-ьko	—