Dragged out my giant red "horse chestnut" beads - the ones that I remember producing a suspicious carmine stain - and re-tested them with Simichrome and a Sunshine polishing cloth, and this time I could not get any red color off them. They did turn the Simichrome to ochre.

So we'll go with heat treatment to turn yellow phenolic to red...although I still think the phenolic itself could be dyed during its production.