Actually, they're available in many different colors, not just green.
From the release:
The crystals that form in the fields around the Namasia ruin appear to have formed naturally. As wide and as high as a man's chest, they are hard enough and plentiful enough to be used as defensive structures against even the strongest modern weapons.
Available in many colors!
The Crystal Field defense line set is carefully cast from high quality clear or colored translucent urethane resin.
Set includes four (4) 5" (127mm) long wall segments and four (4) 2" (50mm) short wall segments.
Placed end-to-end, the total length is 28" (711mm).