Brown lemonade? You don't think your mam was tricking you into thinking old tea was in fact fizzy pop?
Ah, yes. If you haven't tried it, you really ought to. Looks like watery coke, tastes like "normal" white lemonade. There's a useful wiki entry which explains it much better than I would. I am not sure that the shipyard explanation is anything more than urban legend, though.
Is brown lemonade the same as red lemonade? I'm from Ireland, just south of the border and this is the first time I've ever heard of brown lemonade - even though my mother's from Belfast and I went to uni there!