whetstone, polish
礪 centers on a whetstone used for sharpening and polishing blades or tools. The polish sense extends naturally from the action of refining a surface with a stone.
礪 combines 石 (stone) with 厲, which likely contributes the sound and the idea of a rough or grinding action, together suggesting a whetstone.
The left side is a stone 石, and the right side 厲 looks like a complex tool with a rough surface. Picture a coarse stone block used to sharpen and polish a blade until it gleams.
For レイ, imagine laying a blade flat on the whetstone: lay -> レイ, and the stone polishes the edge as you lay it down.
dark brown; reddish brown; polished brown