@Section
   @Title { Colour }
   @Tag { colour }
@Begin
@PP
Colour is obtained in much the same way that fonts and language changes
colour. @Index @Code "@Colour"
color. @Index @Code "@Color"
are, using the @Code "@Colour" (or equivalently {@Code "@Color"}) symbol:
@ID @Code "grey  @Colour  { Hello, world }"
produces
@ID grey @Colour { Hello, world }
The @Code "@Colour" symbol will accept any of the following colours:
@QD @HAdjust @Tab
    vmargin { 0.5vx }
    hmargin { 0.2c }
    @Fmta { @Col A @Colour @FilledBox ! @Col @Code A ! @Col !
            @Col B @Colour @FilledBox ! @Col @Code B ! @Col !
            @Col C @Colour @FilledBox ! @Col @Code C        }
    @Fmtb { @Col A @Colour @FilledBox ! @Col @Code A ! @Col !
            @Col B @Colour @FilledBox ! @Col @Code B ! @Col !
            @Col                      ! @Col                }
{
@Rowa A { darkred	} B { red		} C { lightred		}
@Rowa A { darkgreen	} B { green		} C { lightgreen	}
@Rowa A { darkblue	} B { blue		} C { lightblue		}
@Rowa A { darkcyan	} B { cyan		} C { lightcyan		}
@Rowa A { darkmagenta	} B { magenta		} C { lightmagenta	}
@Rowa A { darkyellow	} B { yellow		} C { lightyellow	}
@Rowa A { darkgrey	} B { grey		} C { lightgrey		}
@Rowa A { darkgray	} B { gray		} C { lightgray		}
@Rowb A { black    	} B { white		}
}
Monochrome output devices will render them as shades of grey.  Colouring
something @Code white makes it invisible (unless printed on a coloured
background), which is sometimes useful.  See Appendix {@NumberOf morecolours}
to get many more colour names, using the @Code xrgb include file
and its @Code "@Xrgb" symbol.
@PP
In addition to the list of colours given above, there is a special
{@Code nochange} colour which produces whatever colour you already
happen to be using; you can also use an empty object to ask for this.  And
you can get lots more colours by specifying them using numbers, like this:
@ID @Code "{ rgb 0.5 0.5 1.0 } @Colour { Hello, world }"
which means use red at intensity 0.5, green at intensity 0.5, and
blue at intensity 1.0, producing
@ID { rgb 0.5 0.5 1.0 } @Colour { Hello, world }
In the strange world of colour coordinates, in which 0 is dark and 1 is
light, this is a light blue.  You can also use the CMYK system:
@ID @Code "{ cmyk 0.5 0.5 1.0 1.0 } @Colour { Hello, world }"
produces
@ID { cmyk 0.5 0.5 1.0 1.0 } @Colour { Hello, world }
Wherever in this document it says that that you can use any colour
from this section, it means any of the names above, or {@Code nochange},
or an object beginning with @Code "rgb" or @Code "cmyk" as shown.
@PP
Whether the colours produced by @Code "@Colour" actually
correspond with the names depends on the output device; the same
nominal colour can look quite different on screen and on paper.
@End @Section
