Getting black objects from vertex.setFill()

I'm trying to color 3D PShape. if I perform vertex.setEmissive(color) on each vertex this does color the object as expected but this is simply emissive color unaffected by the scene lighting. if instead I try to use .setFill() or .setTint() or .setAmbient() on each vertex I get a completely black and opaque object. if I don't do anything at all then the object has a white or gray fill that does respond to the scene lighting.

I don't understand what I'm doing wrong. How do I assign a color to each vertex in a PShape???

DETAILS: I read in a .obj file which creates a PShape object that is simple a list of GROUPs in which each group contains 3 verticies (a triangular face).

I then iterate over this list of lists setting the color of each vertex with the outcome described above.

My thinking is that I must not understand what setFill or setTint or setAmbient do. I'd like to know. But I'd also like to know how to do what I want which is to paint the faces.

here's a code snippet that I'm using:

        sts = p.loadShape("stshuttle.obj");
        sts.rotateZ(p.PI/2);
        sts.rotateY(-p.PI/2);

                    // loop over the list of GROUP PShapes
        // set odd faces red and even faces yellow

        for (int i =0; i<sts.getChildCount();i++){  

            PShape foo = sts.getChild(i);
            int colr2 = (0==i%2)? 0xFF1000 : 0xFFFF00;

                           // loop over all three of the verticies in the GROUP.
            for (int j = 0; j<foo.getVertexCount();j++) {
                     foo.setFill(j,colr2);   // This turns it black 
            //  foo.setEmissive(j,colr2);  //  works as expected
                            //      foo.setTint(j,colr2)   // this turns it black.

            }

        }