Source: CadillacSource: CadillacThe Cadillac Celestiq flagship sedan-wagon-thing is a car that raises many an eyebrow for its design and bespoke nature, and the brand is going further with its latest one-off "Night Test" variant for a very lucky (and well-off) buyer.Debuting for Monterey Car Week, a sole customer spec'd out this particular Celestiq with Caspia Tricoat Metallic paint with a Backen Black and Sheer Gray interior.Source: CadillacSource: CadillacAdvertisementAdvertisementA big part of the Celestiq's appeal (what there is of it, to those who can afford it) is the ability to personalize the color palette to the Nth degree. This "Night Test" unit goes to the opposite end of the brightness spectrum. It's draped in Caspia Tricoat Metallic paint, dark-finish 23-inch wheels, and a Jade lighting bezel. Cadillac says it has a "stealthy dark finish, diffusing light instead of reflecting it."Source: CadillacSource: CadillacThings lighten up inside. Though the overarching color palette is fairly monochromatic, the Backen Black and Sheer Gray Leather mate with carbon-fiber and brushed-metal accents. Cadillac says this makes it "feels like a precision instrument."Just like every other Celestiq, the bespoke Night Test one-off car is hand-assembled at the Cadillac Artisan Center in Warren, Michigan. Cadillac didn't just let the buyer go for gold with the design, instead lending a helping hand for an "individually curated palette of colors, materials and finishes." Though this car isn't for sale-it's going to the well-off buyer-those who want to take a gander can see it at The Quail, A Motorsports Gathering, during Monterey Car Week.Become an AutoGuide insider. Get the latest from the automotive world first by subscribing to our newsletter here.