This page provides information on the V-Ray Vertex Colors Map.
Color set – Connects the color set name of a mesh. This connection is only used if the Type parameter is set to Color Set connection. Use the Connection editor to connect a mesh's colorSet[index].colorName plug to the colorSet plug of the vertex color texture.
Type – Specifies how the vertex color texture will detect the color or UV set to use.
Set name – Used when Type is set to Set name. Enter the color or UV set name as specified in the rest of Maya's UI. The appropriate color/UV information will be found based on the objects that have this vertex color texture assigned as part of their shading network(s). This allows the ability to create a single VRayVertexColors texture to be used by many meshes as long as their color/UV sets share the same name.
Use UV set – When enabled, the Set name will be searched in the list of UV sets instead of the list of color sets. The values of the UV coordinates will be directly used as colors.
Set Index – Used when Type is set to Set Index (V-Ray proxies only). V-Ray proxies exported from 3ds Max that may be used in Maya may not have color/UV set names information. In that case, the user will need to set the value of this parameter to the exact index of the corresponding set when it was exported from 3ds Max. Note that this index is 0-based.
Default color – Specifies the color to use for vertices/faces that don't have color information. Note that a texture can be used here.