Vintage Grand Seiko runs deep with a varying multitude of case shapes, dials, movements and bracelets, there are dozens of options and references. The 5645/6-8000 came in two variants; silver and a linen textured dial, with the latter being shrouded in a bit of speculation.
Originally, this grey linen dial was actually a rich dark blue. It’s been widely accepted that over time nearly all dials coincidently faded to a uniform grey tone. This is merely a theory but to support it are a few “new old stock” 5645/6-8000’s that have been discovered over the last 5-6 years which still displayed a rich, dark blue linen dial.
Speculation aside, this here is an excellent grey-dialed example with a bit of Seiko lore tied directly to it. It appears unpolished and sports only light general wear throughout the case and original bracelet.