Hi Roberto, All helmets pre 1943 should be painted khaki green, either textured outside & smooth in 1938-41.Then textured inside & out 41- to maybe early 43, hard to tell exactly as with textured paint you can't read the date/maker, but have seen a 42 dated khaki green textured inside & out.
1943 saw the first use of textured dark brown on the Mk2, & like the khaki green of the previous year 1942 it would have been textured inside,why go back to the old way.
I have also seen early Mk2's pre 1939 textured dark brown inside & out with post war liners, adding to what we know that they were refurbished post war. As some units were still using the Mk2 into the 1950's.
As we have little information on WW2 British helmets, ( when are these promised books coming out) that for me your one has been refurbished post war, but as said with so little information could some have been refurbished & painted dark brown during the war?