Another line-up of Ki-21 Model 1s from the Hamamatsu Bombing School, this time in a colorized photo.
The bomber in the foreground has a very low serial number; "120". If that's true and there are no missing digits, then it's a Mitsubishi built Model 1 Ko.
Note the three fuselage bands on the "Sally" next to "120". Only the Hamamatsu school used bands like these to differentiate the individual bombers. Ofcourse, also note the overall hairyokushoku, not "silver", finish of the bombers.