Hello,
Regarding of practical use of RLM 83 Dark Blue I just find this:
http://www.aircrewremembrancesociety...177/index.html
At color description of the Johann Dreher's downed plane, a Junkers Ju 88G-6(Werke/Nr.621586? other sources give as 620028), in Operation Gisela on 4 March 1945 is stated: Markings- D5 (small) + AX (both black). Undersurface light blue, mottled with white, continuing up the sides of fuselage and fin. Upper surfaces
dark blue mottled with grey and white.