Author: Jonas Bilinkevicius

How can I make the font color dependent from the background color? I want to make 
the color selection between white and black dependent from the background color.

Answer:

This seems to work pretty well, at least on a non-palette video mode:
1   
2   function InverseColor(color: TColor): TColor;
3   var
4     rgb_: TColorref;
5     function Inv(b: Byte): Byte;
6     begin
7       if b > 128 then
8         result := 0
9       else
10        result := 255;
11    end;
12  begin
13    rgb_ := ColorToRgb(color);
14    rgb_ := RGB(Inv(GetRValue(rgb_)), Inv(GetGValue(rgb_)), Inv(GetBValue(rgb_)));
15    Result := rgb_;
16  end;
17  
18  procedure TForm1.Button1Click(Sender: TObject);
19  begin
20    with colordialog do
21    begin
22      color := label1.color;
23      if execute then
24      begin
25        label1.color := color;
26        label1.font.color := InverseColor(color);
27      end;
28    end;
29  end;