Hi Vitor,
there is a brownish variant of the interior/metal panel paint recorded for some German aircraft (notably LVG-built, but possibly more) - mentioned by Dan-San Abbot and others. This has a a Methuen notation of 4C3 (i.e. beige, greyish-yellow, or light blond) and a very decent match can be easily achieved with a 50:50 mix of Gunze H336 (RAF Hemp) and H311 USAF Gray FS36622. Suitable at least for Alb DII (LVG), the LVG C series and DFW CV (LVG).
Cheers,
GrahamB
Note: ratio for these two is not 50:50 (brainfade!) but 3:1