Tangent, but for all we whinge about flat UIs and pine for the bezelled good old days, that colour picker from the oldest good old days is really bloody flat!
It was flat, yet designed well in the sense that one can tell which things are clickable, which areas scrollable, etc. Contrary to many modern flat UIs that don't even show the scrollbar upfront so you just have to "feel" when something is scrollable or not, don't distinguish between links and buttons, and so on.
It also manages to give controls "breathing room", yet not waste too much space on margins and paddings.
https://www.engineersneedart.com/blog/almostfired/HSL_RGB_Pi...