Not named just for their colour, brown ales have had a very up and down progression through time.
Starting in the 17th century British brewers began brewing brown ales as a step up from the popular amber ales of the times. They had varying strengths of alcohol and were mildly hopped. In the 18th century they declined in popularity as advances in technology made kilning easier. Brewers shied away from brown malt in favour of the cheaper and more yielding pale malt which would be then used in the creation of Porters and Stouts.
In the 1920’s the style started to become widely brewed again though it had a reputation as being a working class beer thus setting itself apart from the office culture of paler beers. During WWI raw ingredients became highly sought after in the war effort and the British Government made a push for weaker beers. Strong beer also equated to beer that lasted longer so bar keeps had to get creative; by using bottled brown ale from their supplies and mixing it with the weaker beer they were able to keep their customers happy and drive up demand for the brown ales.