Where does “鼠色” come from?

鼠色 (Japanese) comes from Japanese 鼠, from Japanese nezumi.

鼠色 (Japanese): gray

Definitions

Step	Language	Word	Meaning
1	Japanese	鼠	a mouse or a rat; general term for members of...
2	Japanese	nezumi	—

鼠色 — Etymology, Origin & Word History | Etymology Explorer