"The dark section, for night hours, features luminous numerals, while on the white section of the bezel, for day hours, it is the background that is illuminated to contrast with the dark numerals. Pretty cool. Also, Grand Seiko deliberately divided the bezel in an unusual way, not precisely in half – but at 6:30 and 17:30 – so the numerals are not split."
So to illuminate the bezel and have it bi coloured it only works asymmetrically. I would not describe this as "pretty cool" but as a weird compromise.They could not manufacture the bezel correctly. As my reply above, GS went to market with a product without solving a fundamental design flaw.