How to draw outline only of generic Cesium Primitive

1. A concise explanation of the problem you're experiencing.

I am drawing cesium primitives using vertices and indices that I create and using the most generic kind of Cesium Primitive, a Cesium GeometryInstance of a Cesium Geometry that is created using vertices and indices that I create. I use a primitiType of TRIANGLES on the geometry. It renders fine as faces, but how can I render this primitive in outline form?

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

this.scene.primitives.add(new Cesium.Primitive({
  geometryInstances: [geoTransformed],
    appearance: new Cesium.PerInstanceColorAppearance({
    translucent: true, //was false
    closed: true
  asynchronous: false

where geoTransformed is

const geoTransformed = new Cesium.GeometryInstance({
    geometry: new Cesium.Geometry({
        attributes: {
        position: new Cesium.GeometryAttribute({
          componentDatatype: Cesium.ComponentDatatype.DOUBLE,
          componentsPerAttribute: 3,
          values: vertices
      primitiveType: Cesium.PrimitiveType.TRIANGLES,
      boundingSphere: Cesium.BoundingSphere.fromVertices(vertices),
      vertexFormat: Cesium.VertexFormat.POSITION_AND_NORMAL

      attributes: {
        color: Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.AQUA)
      id: 'transformed'

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

This code renders the solid primitive nicely, but I want the outlines only.

4. The Cesium version you're using, your operating system and browser.
Cesium "1.48.0",
chrome Version 71.0.3578.98 (Official Build) (64-bit)

Are you trying to render the outline of everything (like a wireframe) or total outline of the shape (like a silhouette) ? If it’s the latter, these Sandcastles have examples on using outlines like that: