Sets the transparent
color used as the "chroma-key" on video overlay hardware (has the same effect
as specifying GRAPHIC COLOR integer). The color is set as a numeric
value in the range 0 - (n-1) where n represents the number
of colors available. This value only pertains to video overlay devices,
such as Video Blaster.
The default value is determined by the user through the Setup page for the
digital video device; if a default value is not set by the user, 0x2D becomes
the default.