Default halo color is close to ffd800.

Selection halos on spacefill automatically adjust to remain visible regardless of the spacefill
radius or zoom.

For backbone/wireframe, the halos disappear at high zoom, and don't resize for different radii.

Therefore, best is to spacefill same radius as backbone/wireframe for selection halos on those.
See jmol user correspondence April 26, 2021.
