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  In an effort to make the graphics modes compatible with a wide range of
  monitors, both color and monochrome, IBM included a few modes on the Color
  Graphics Adapter that do not produce color: color-suppressed modes. There
  are three color-suppressed modes: modes 0, 2, and 5. In these modes,
  colors are converted into shades of gray, or whatever color the screen
  phosphor produces. There are four gray shades in mode 5, and a variety of
  shades in modes 0 and 2. CGA's color is suppressed in the composite output
  but not in its RGB output. This inconsistency is the result of an
  unavoidable technical limitation.

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  NOTE:
    For each color-suppressed mode, there is a corresponding color mode, so
    modes 0 and 1 correspond to 40-column text, modes 2 and 3 to 80-column
    text, and modes 4 and 5 to medium-resolution graphics. The fact that
    modes 4 and 5 reverse the pattern of modes 0 and 1 and modes 2 and 3,
    where the color-suppressed mode comes first, has led to a complication
    in BASIC. The burst parameter of the BASIC SCREEN statement controls
    color. The meaning of this parameter is reversed for modes 4 and 5 so
    that the statement SCREEN,1 activates color in the text modes (0, 1, 2,
    and 3) but suppresses color in the graphics modes (4 and 5). This
    inconsistency may have been a programming error at first, but it is now
    part of the official definition of the SCREEN statement.
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