Swiss Stamp Zumstein 24

The number Zumstein#24 (airmail) /Scott#C25/ Michel#293 presents 4 shades of overprint
24a= light red
24b= red
24c= dark red
24d= dark carmine red

I am interested to see the difference between these shades and in particular between 24a and the other ones.
If somebody has the 24a and another shade (24b, c, d), can he put here a scan of these stamps?
The best, of course, will be a scan of the 4 shades, one next to the other.
I thank him very much.

Certified by Marchand as Mi 293a:



I'm sorry but I don't have the others for comparison.

Thanks