Color Operations

A color can be represented in two ways: as a color index or as a rgb value. All drawing functions which take a color argument accept colors in both forms. An rgb value is assigned to and index with change-color.

•   (make-rgb red green blue)
  make-rgb takes three values in the range 0 (dark) to 1 (bright) and returns an rgb (a color).
•   (rgb-red color)
  (rgb-blue color)
  (rgb-green color)
  rgb-red, rgb-green and rgb-blue return the red, green, and blue components, respectively, of a color.
•   (rgb? color)
  rgb? reports whether color is a valid color.
•   (change-color index rgb)
  change-color changes the color at index in the color table to the color specified in rgb.
•   (default-display-is-color?)
  default-display-is-color? returns #t if the default display screen for viewports is in color or #f otherwise.