MiG-21 MF "Grey"
The MiG-21 MF "Šedivka" was a subversion of the MiG 21 MF produced in the Gorkov Aviation Plant and which differed in some technical parameters from the standard version of the MiG-21 MF and its correct designation was the MiG-21 MF-75. Basically, it was a transition type between the MF versions (referred to as Type 76) and the BIS (referred to as Type 75), and the main visible differences in the cockpit include a different design of the boxes next to the sight, moving the warning signs from the right part of the main dashboard to the right side panel and a different shape of the ramp head (the straight upper part of the ramp of the MF version is replaced by a stepped head in the case of "greys", where the trim control is extended above the other controls). A total of 20 machines of this type were delivered to the air force of the then Czechoslovakia and after their delivery to Czechoslovakia, they were deployed at the air base in České Budějovice at the 1st column. The first four machines were delivered on 2.7.1975, the remaining machines were flown over from the Soviet Union on 17.9.1975. It is interesting that the machines were flown without their royal emblems and hull numbers, which were applied by painting, not spraying, in the repair shops of the base in České Budějovice. These were fuselage number machines:
2205 2500 2410 3008 4003
4008 4017 4038 4101 4127
4175 4307 4405 4421 5494
5508 5512 5581 5603 5612
At the same time, by coincidence of further development, these were also the machines from which aircraft intended for conversion to the MFN/RNAV version, a version equipped with communication and navigation means enabling cooperation within NATO structures, were recruited, and which ended in 2005 the decades-long deployment of MiG 21s in the Air Force of the Czech Republic, or Czechoslovakia at that time.
You can find a lot of detailed information in the fantastic book by Mr. Rogel and Mr. Martínek "Grays – a little different MiG 21 MF in our air force" published by Svět křídel.