Multi Material

doc.bjs.com - How To use Multi Materials

[
    {
    "mesh3" : {
        "material" : {
          "subMaterials" : {
            "0" : {
              "diffuseColor" : "yellow"
            },
            "1" : {
              "diffuseColor" : "white"
            }
          }
        }
      }   
    }   
]