Hi Stuart ,
Sorry for the delay in replying , been a bit busy wi`t book !!.
Re : Dark wort (Brown , R/B etc) ; This was done in a few breweries to extend their product range / lines ,with the dark wort usually added with the sugar additions at the tail end of the boil ; IE: Pale, Darker & Stouts etc to get a few beers from one main extract mash . ( Allthough some brewers opted for a small ammount of Patent (Black) malt in the tail end of the boil to darken wort)
2nd ,the dark wort may have been added to the F.V to standardise colour at the end of primary fermentation (Again increasing the range if desired),
Cheers ,
Edd