It's worth noting: Graphics extracted from WormsDC would be lower-quality than those same graphics extracted from Worms United. Utd utilized a single shared 256-color palette for its display, while WormsDC utilizes multiple smaller palettes per-layer to get to 300+ colors.
As a breakdown, DC uses 16 colors for the terrain - a palette it also shares with sprites, with the color of worms, grenades, crates and mines determined by color values in the terrain/map file. Then there's 16 colors for the first layer of mountains, then another 16 for the back layer. I suspect each layer of water also uses 16 colors apiece, but when creating a terrain you're only picking the base color of the water using RGB values, and it extrapolates the rest from there. Ditto the sky gradient.
Utd, meanwhile, has a fixed 256-color palette which is used across all of its terrains.