I'm really not a fan of brutalism (in UI and in architecture) and I think that our monitors have 24-bit color depth for a reason. Such extreme simplification of UI is not the way I think.
(Microsoft has attempted this in Metro, but quickly withdrew from this idea)
Microsoft's Windows 8 era "Metro" guidelines were extremely colorful. They often emphasized one single brand accent as a standard across an app, but it could be just about any color you wanted. Or one single accent color of the user's choice to give them a sense of personal ownership. They also emphasized the importance of "full bleed" photography and what a colorful wallpaper with basic parallax effects can do to make an app seem alive.
Most of the really vibrant "magazines" and apps and "hubs" only ever really existed on Windows Phones at that time and most desktop apps stuck to a bare minimum so most people missed all the good colorfully and playfully vibrant examples of what those UI guidelines could be when done right.
Maybe in theory it was colorful (I've never read the actual design documents), but in practice the complexity of "legacy" multiple-color controls that were 3d and gradiented was switched to extremely simplified, mono-color equivalents which made me wonder if what I'm about to click is a control or just a simple text label.
I've never used Windows Phone as well, so I can't compare to how Metro looked on those devices. I only know what they've done with Metro on Windows on PCs.
(Microsoft has attempted this in Metro, but quickly withdrew from this idea)