british paint on WW2 tanks

Slopped darker brown? Never heard of that. Perhaps it is meant as brown apllied over the desert yellow as cammo. An article on Stuart cammo in an old FSM shows one with 4 colors: Dark Green, Slate Grey, Light Stone and Olive Drab. This was applied to a Stuart during Operation Crusader Nov. 1941. Sorry, no help here.

yeah, i hadn't either.... was wondering

As a camo colour, the darker brown could have been applied that way, although I would imagine the Brit troops were a little more refined than to get into finger painting. It depends on what time the vehicles are depicted as the schemes changed year by year:

In July 1939 orders specified a base tone of Middle Stone with disruptive patterning of Dark Sand.
1940 saw the 3 colour Caunter Scheme in use.
1941 saw the two colour again: Portland or Light Stone as the base with Dark Olive Green (SCC7), Silver Grey or Black pattens over that.
October 1942 the scheme was changed again, to a base colour of Desert Pink with a pattern of Dark Olive Green. Black, Very Dark Brown and Dark Slate were also used in lieu of the green according to some references.