I live next to the Thames, that is pretty much brown most of the time. However it doesn't mean I expect all rivers to be brown. The majority of aerial shots I've seen of inland waterways are pretty much what is being shown to us here by Genndich.
It looks pretty superb to me, the banks slipping into the murky depths of the river with a faint reflection of clouds on top....and if Copterdrvr says it looks real, then that is good enough to me, he flys helicopters and should know

Me I'm just pleased that we are getting, what looks to be, a decent WWI sim, everything else is a bonus