UseColorMask - Render is different from Rendered Viewport & CaptureToFile

As said, it will be in Rhino 8.1. As mentioned a couple of days ago the Beta is closed now Rhino 8 WIP Available Now! - #130 by brian , Rhino 8.0 is already available for evaluation if you want the latest version. If you get that evaluation version and set to get service release candidate (SRC) of Rhino 8.1 as update frequency you’ll get the fix already next week Tuesday (assuming we release a SRC then).