Is there a system-defined NSColor for the background of an NSBox? Testing shows it to be RGB (226, 226, 226) but there does not seem to be anything like controlBackgroundColor for it to easily switch when in Dark Mode. I am using this color for the background of a custom NSView and don't really want to embed the view in an NSBox to get the effect I want.
From the AppKit Release Notes, the fillColor of a custom NSBox is set to controlBackgroundColor, windowBackgroundColor, or underPageBackgroundColor, but those aren't the same as the background for a default NSBox.
I asked this same question earlier in Apple's Developer Forums (also looking to provide a dark mode color), and aside from the usual boilerplate responses, the answer was that there is no system color name for it. The standard control and gray colors are a bit darker, so if you want to match the default you will need to roll your own.