First I have masked the observer seat, then airbrushed light grey (Gunze H325) on the elements of the cockpit interior: as previously said, crewmen asked that the alu color of the interior was repainted in grey due to the reflection of light.
Then I removed the masking tape and applied generously Mars Brown oil paint. After 1/4 hour, I removed the paint with a brush, slowly, patiently... Result sounds good. Now I have to paint seatbelts and details...