One of the most impressive was the H6K (Mavis). The first planes that left the production lines in 1938-1939 were in Natural Metal Finish like the plane in the photo below from a vintage magazine.
Once they started serving in the South Pacific front and following orders from the IJNAF regarding camouflage, Mavis became green-top, gray-bottom like the example below from a caption of a war news film.
Below is an artwork example.
And some beautiful artwork by Koike Shigeo of a civilian Mavis operated by Dai Nippon Koku K.K.
After the end of the war a couple Mavis were found in Yokohama as shown in the NARA photo below.
I think that the Mavis in the foreground is also in the photo below offering a clear top view.
Another rather interesting Mavis found after the end of the war is the one below.
this and according to the caption:
"Mechanics of 3219 Servicing Commando, Royal Air Force (RAF), check the engines of a Japanese Kawanishi H6K 'Mavis' flying boat at Sourabaya (Soerabaja), Java, in preparation for an air test flight. Of interest are the markings added by Indonesian nationalists and the fact that an additional band of blue has been added to the fuselage marking by the Dutch."
Note that the hinomaru on the fuselage and the wing are erased. Instead it has a Dutch flag on the fuselage and an Indonesian red/white marking under the wing. Note that it also used to have surrender crosses on the fuselage and under the wing (outlined in red); the one on the fuselage seems to have been also erased.
So what could the overall color be? Some mention that it was "silver" even though it would have an extremely rare exception since all Navy planes flying in the South Pacific were camouflaged by necessity. Others suggest that the whole paint of the plane was removed. But that would mean a very long and tedious process with no apparent reason.
The same Mavis later received British roundels and ATAIU SEA markings on the fuselage sides and was transported to Seletar base in Singapore as can be seen in the e-bay photo below (sorry for the poor quality).