Where does “สีไม้” come from?

สีไม้ (Thai) comes from Thai ไม้, from Proto-Tai *mwajꟲ.

สีไม้ (Thai): coloured pencil

Definitions

Step	Language	Word	Meaning
1	Thai	ไม้	wood; stick; log; tree; plant; mark
2	Proto-Tai	*mwajꟲ	—

สีไม้ — Etymology, Origin & Word History | Etymology Explorer