From the manufacturer:
Dark Clay is a muted grey color with a green tint. Combine it with black shading and you can put an opaque skull together in no time.
This color looks amazing when doing murky, swamp looking environments and works great as a background shadow for trees, leaves, and more!
You will get a nice unique color when mixing with Florida Moss
Gauge Size
The gauge size is the circumference of the smaller bar in the middle.