Color is indicative of plug temp, not (directly) A/F mixture.
It's the thickness of the ring at the bottom of the insulator that's the telltale of A/F. The darkness of the ring comes with more time. The lighter of wibby's plugs are about 8 sec, the darker about 15 sec.
But..it's the thickness or depth of the ring that's the issue. The 155 is still pretty wide. The 152 is pretty light, but it looks wide (not quite as wide), too.
Hey! No shiny bits! Good deal!