When looking at screenshots of Windows 1.0, you can see the dithered green as defined as default here. However, the actual color representation was highly dependent on the graphics adapter and also the CRT used. That means, what looks like a very bright cyan-green is the pure software side with todays sRGB faithfulness and quite possibly differs vastly from how it looked back in the day - and it might also have differed then, depending on the hardware used. Nevertheless, this is how it would look today, when emitting the same color on modern hardware.