RGB: red green blue composite colors (H)

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Build a color value from its primary components:
- color = RGB( red, green, blue [, indx] )
the option indx=24...31 sets the
predefined_color
(indx) to the red, green, blue values given, so that it can be used like the indices 0...23 ⇒ Colors.
with the use of indx the color value defined by RGB is saved
- indx ≤ 24 sets color(24)
- indx ≥ 31 sets color(31)
the actual representation of a color is dependent upon the Windows configuration where it is displayed.
the maximum value for each argument is 255, e.g.:
- black = RGB( 0, 0, 0)
- red= RGB(255, 0, 0)
- yellow=RGB(255, 255, 0)
- white = RGB(255, 255, 255)
- lightblue=RGB(166, 202, 240, 31) ! sets the predefined color 31 to lightblue
- Both, lightblue or 31, can be used as options in HicEst function calls, e.g.:
  - WRITE(BaCkcolor=black, ForeColor=31) string ! write to screen
  - WRITE(BaCkcolor=black, ForeColor=lightblue) string ! same result