OK. I have found a nice shot of the Tempest on an assembling line in a factory. As you may notice the fuselage is already camouflaged. Also at the area behind the armour plate. There is a lack of the sealing "collar". The black colour can be noticed on the supports for the armour plate and the front mount for the guide rail only. The guide rail was attached later and for sure , was painted separately, not necessarily with the black. In the second pic you may notice the black paint applied behind the armour plate up to the "collar". The guide rail looks like being of the camouflage colour but not of the black. The third shot is the enlarged one of the JF-G and JF-M kites. Also here can be noticed that the rail is lighter than the black painted area between the armour and the collar. Especially it can be noticed nicely at the front area of it where the front mount is. The horizontal surface of it is clearly lighter than the black one around.
the pic source: the net.