This schematic on the subject of Aichi M6A1 Seiran (Navy Experimental 17-Shi Special Attack Aeroplane) colours was prepared in response to a private request and may be shared here. The colours are as measured and recorded on the surviving NASM example by Robert C Mikesh and documented in his article 'Japanese Aircraft Colors at NASM' which appeared in Vol.3 No.1 of the Asahi Journal and also in the Seiran feature of his book 'Japanese Aircraft Interiors 1940-1945' (Monogram Aviation Publications, 2000).
Regarding the interior colours Mr Mikesh noted that they predominantly approximated the Thorpe identified colour N2 which has been matched to Munsell value 10 G 3/2 (see Thorpe Colour Table).
In his monograph on this type in the Monogram Close-Up series published as #13 'Aichi M6A1 Seiran' (Monogram Aviation Publications, 1975), Mr Mikesh identified the upper surfaces as being 'Dark Green' Munsell 10G 3/2 with the lower surfaces as 'Light Grey' Munsell N 7.5 and the interior as 'Olive Green' Munsell 10 Y 4/4. The latter value Munsell 10 Y 4/4 is the colour identified as N5 'Light Olive Green' by Thorpe.
Mr Mikesh also authored two earlier booklets on the subject of Japanese interior colours in the Monogram Close-Up series as #14 and #15 respectively, 'Japanese Cockpit Interiors', Parts 1 and 2, (Monogram Aviation Publications, 1976). In this publication he identifies Munsell 10 G 3/2 as 'Exterior Navy Green' and notes that there is no close FS 595b equivalent to it. The closest is actually 34058 @ 3.99 but it is too blueish in appearance (a value of 2.0 or less equals a close match).
An excellent account of the last operational use of Seiran may be found in 'I-400 Japan's Secret Aircraft-Carrying Submarine - Objective Panama Canal' by Henry Sakaida, Gary Nila and Koji Takaki (Hikoki Publications, 2006). The type is also covered in Ryusuke Ishiguru and Tadeusz Januszewski's superb 'Japanese Special Attack Aircraft & Flying Bombs' (Mushroom Model Publications, 2009) reviewed here.
Image credits: Seiran colour photograph Mark H Brown/USAFA via author; Rendered colour chips © 2009 Straggler incorporating original Kariki 117 paint standard plates.