I dont know if there are any predefined functions to do this but TColour's (sorry TColor's) are just Integer values the Top 8 bits define other attributes but the low 24 define the colours
In hex $FFFFFFFF is white, so provided you mask the top two nybbles you can do Bitwise manipulation of the values
OR, AND, XOR each of the 3 lower Bytes is a colour.
I haven't bothered with the masking but this works.
You get a purple panel.
procedure TForm1.Button1Click(Sender: TObject);
var C1,C2,C3: Tcolor;
begin
C1 := CLRed;
C2 := ClBlue;
C3 := C1 or C2;
Panel.Color := C3
end;
Hope this helps
Steve.