protected void updateMatParamOverrides() {
        refreshFlags &= ~RF_MATPARAM_OVERRIDE;

        worldOverrides.clear();
        if (parent == null) {
            worldOverrides.addAll(localOverrides);
        } else {
            assert (parent.refreshFlags & RF_MATPARAM_OVERRIDE) == 0 : "Illegal mat param update. Problem spatial name: " + getName();
            worldOverrides.addAll(parent.worldOverrides);
            worldOverrides.addAll(localOverrides);
        }
    }
Should be overridden by Node and Geometry.
jme3-core/src/main/java/com/jme3/scene/Spatial.java