const sphere = new THREE.Sphere(intersection, radius);

// now checking if each vertex of a face is within sphere
// if all are, then color the face at index i
for (let i=0; i < (positionsAttr.count) /3); i++) {
  vertexA.fromBufferAttribute(positionsAttr, i * 3 + 0);
  vertexB.fromBufferAttribute(positionsAttr, i * 3 + 1);
  vertexC.fromBufferAttribute(positionsAttr, i * 3 + 2);
  if (sphere.containsPoint(vertexA)
    && sphere.containsPoint(vertexA)
    && sphere.containsPoint(vertexA)) {
    colorFace(i);
}