"X will not run in these 4-bit overlay planes. This is because I’m using Motif, which is so sophisticated it forces you to put a 1” thick border around each window in case your mouse is so worthless you can’t hit anything you aim at, so you need widgets designed from the same style manual as the runway at Moscow International Airport."
A big contributing factor to Motif's profligate palette consumption was the bevels to make it look "3-D". I think Motif was actually an inept attempt to ape the aesthetically uninspired Microsoft Windows, which was not very popular yet, but which (relevant here) ran fine on 4-bit displays. Because that's what the VGA gave you in 640×480, and a Windows that limited you to 320×200 or 640×200 on a VGA would have been a non-starter.
Open Look had a bit of a 3-D look to it, but for example (original) Macintosh and Genera were pretty flat-looking. GEOS was mostly pretty flat with the exception of the occasional drop shadow. The Newton GUI (postdating Motif) managed to get quite a bit of visual depth out of grayscale, but I don't think the Newton ever had a 1-bit display. The Palm Pilot (postdating Newton) looked like a less ugly GEOS.
In theory there are all kinds of depth cues you can use to get a comprehensively 3-D look on a 1-bit display, but I haven't found a GUI toolkit that managed it.