This is the Woodland Scenics CW4532 Hunter Green Water Undercoat.

CW4532 - Water Undercoat™ - Hunter Green - 3.75 fl oz (110 mL)

Specially formulated to represent authentic colors on the Forel-Ule Scale, Water Undercoat lays a base for creating dark depths to shallow shorelines, and underwater scenes for any aquatic ecosystem. Create customized colors by mixing Water Undercoat together.