Windows 1.0 (1985) was Microsoft's first graphical shell, running tiled windows over MS-DOS. Limited to a fixed hardware palette, it couldn't display its signature desktop green directly — so it dithered it, tiling 8×8 blocks of bright green with 4×4 patches of cyan to blend a softer shade the hardware couldn't name. Depending on how you average that pattern, the result lands near #57ff81 (a simple pixel average) or #57ff9a (averaged in linear light, gamma-corrected).
The Windows 1.0 desktop. There was no single green for it in the hardware palette, so the desktop was dithered — 8×8 blocks of green (#57ff57) with a 4×4 patch of cyan (#57ffff) inside each, 25% cyan by area. This is the conventional pixel average of that pattern; averaging in linear light instead gives the gamma-corrected #57ff9a.