Apparently, when you connect an analog monochrome monitor to a VGA adapter, the VGA adapter automatically translates color information into monochrome information through "color summing." Because all of the three primary colors (6-bit) are being combined to form a grayscale value, you can only get 64 shades of gray.

Many Sierra games, for example, support grayscale graphics that I was never able to get running on my old PC, which had a color analog monitor. But when I counted the colors I got something far more than 64! In this case, I assume that Sierra somehow disabled color summing in the VGA and transmitted the raw color values instead and relied on the monitor to do the conversion.

Also, software that uses the monochrome EGA mode 0Fh doesn't work, but software using the monochrome VGA mode 11h does work. A fix or a regression?