Colours an area of the screen.
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 Syntax

       GT_ColorWin(<nTop>, <nBottom>, <nLeft>, <nRight>,;
                <cNewColor>|<nNewColor>, [<cOldColor>|<nOldColor>]) --> NIL

 Arguments:

     <nTop> Top of box

     <nLeft> Left of box

     <nBottom> Bottom of box

     <nRight> Right of box

     <cNewColor>|<nNewColor> Can be a clipper colour string or an integer
     attribute to paint the area with.

     <cOldColor>|<nOldColor> Can be a clipper colour string or an integer
     attribute to indicate which colour to paint over.

 Returns:

     NIL

 Description:

     Paints an area of the screen in a specified colour, optionally
     only over a specified colour.

     Note: The module also includes a C/ASM callable function equivelant
           in the form of:

              void gt_Colorwin (unsigned t, unsigned l, unsigned b,;
                                unsigned r, int c1, int c2);

 Examples:

     // This example will draw a box in two colours and the paint the box
     // lines in white on red by replacing only the white on blue
     SetColor("W+/B")
     @ 10, 20 TO 16, 60 DOUBLE
     SetColor("GR+/B")
     @ 11, 21 CLEAR TO 15, 59
     GT_ColorWin(10, 20, 16, 60, "W+/R", "W+/B")

     // This will paint the whole box in one colour
     GT_ColorWin(10, 20, 16, 60, "W+/G")

 Source: COLORWIN.C

 Author:  Ian 'DrDebug' Day (Dark Black Software Ltd.)