Peterbilt, Kenworth, White, Freightliner, Mack and others purchase frame rails from suppliers, the rails are cut to length and shipped then drilled at the the factory and assembled using proprietary cross members.
(today rails are ordered pre-drilled to the exact specification of each truck). The rails ordered by one truck maker will not be the same as ones ordered by another maker.
Each manufacturer offers different frame section height depending on the intended load/use of the truck. A lightweight highway truck and a large transit mixer will have different frame rails.
As for the assembled frame/chassis, there is no "generic" chassis used by manufacturers, the exception being certain components (crossmembers or spring hangers) shared between rival siblings owned by the same company.
Each manufacturer has a unique way to assemble the frame, and unique bolt/fastener patterns and locations. Each truck maker has unqiue to them front and rear of frame rail treatment as well.
With all that said, in the modeling world you can use about any chassis for a build - but will require modifications for a "true to the make" build.
Since I'm rambling about frames, on the subject of color: None of the class 8 heavy truck manufacturers use flat or matte black paint on their frames. They paint them with gloss paint. The frames look matte because of road grime. There are levels of gloss available, some have a high gloss, some not so much. All of the truck manufacturers would paint the chassis any color the customer wanted. The Big 3 Detroit truck builders had black as standard. The others had "one color on cab, one color on chassis" option - which meant the customer could select a color on the cab and a different color on the chassis as standard. - Historical Peterbilt note: The old butterfly hood Peterbilts - the fenders were attached to the chassis and would get painted with the chassis. Selecting a separate color for the cab would create a nice contrast with the cab one color and the fenders and chassis a different color.