Vertex paint dictates what variation (skin-tight and robe-like) of deformation maps the painted area will deform according to in CAS during body customization and animation.
00FF00 is for skint-tight areas, 3FFF00 is for any skirt-like area ( skirts, bottom parts of dresses, coats, aprons, etc).
Start by choosing 00FF00 and Paint - Set vertex color
1). Disable Limit selection to visible;
2). Holding Ctrl, lasso-select the bottom part of the mesh starting somewhere in the middle of the pelvic bone;
3). Enable sync;
4). Press B and deselect legs;
5). Switch to Vertex paint and enable Face selection masking for painting;
6). Type in 3FFF00;
7). Paint - Set vertex colors;
8). Press A twice to deselect and select everything again, Paint - Smooth vertex colors