javascript - Using Three.js (r78), how to transition line material color between two values along a path? -

i thought understood example, attempt @ applying code produces solid black lines. please me understand why might not working?

function(ptarray) {   var geometry = new three.buffergeometry(),       material = new three.linebasicmaterial({         color: 0xffffff,         linewidth: 4,         vertexcolors: three.vertexcolors       }),       linepositions = new float32array(pts),       linecolors = new float32array(pts),       visible = new float32array(pts / 3);    visible.fill(1.0);    (var p = 0; p < pts; p ++) {     linepositions[p] = ptarray[p];     linecolors[p] = new three.color(0xffffff).sethsl(p/pts, 1.0, 0.5);   }    geometry.addattribute('position', new three.bufferattribute(linepositions, 3));   geometry.addattribute('vertcolor', new three.bufferattribute(linecolors, 3));   geometry.addattribute('visible', new three.bufferattribute(visible, 1));    scene.add(new three.linesegments(geometry, material); }