In my youth LNER brown coach livery was just that, darkish brown. The same, more or less that that house doors window frames and the like were painted in those days. Totally without character. Certainly all the pre-grouping coaches that I recall were the same dark muddy brown. It was only the mainline stock that was different. Those were always in the varnished teak livery, but even that looked dirty brown after a few years in service. The Thomoson teak livery (painted) certainly brightened things up for a while.
As an aside I normally use precision LNER Teak paint for my models but to be honest with myself I have often thought that this was a degree lighter than reality.