Adding a bit to what Superfly said, you are going to have to edit the palette for the file, and you aren't limited to single colors. I edited mine to where the sight is 64x64 and the lines are 3 pixels wide so they are more pronounced in the F4U. The two outer two pixels are orange, and the inner is yellow, which makes for a glowing orange crosshair that is easy to distinguish with either the sky or ground as the backdrop.
Superfly, its not possible to make the sight picture in game bigger is it? When I changed to 64x64 the sight appeared the same size, just with a finer resolution.
Gordo