Water is colorless.
We see it as blue or green or gray or even brown (based on sediments at the base) depending on the sky that moment. It’s the reflection of the sky that we see in the water. However, there have been instances when I have been told that at confluences, there is a distinct difference in color and temeparament of the two (or more) rivers.
I don’t recollect seeing very many confluences. This one above is at Harper’s Ferry where the Shenandoah (from Virginia, seen as clear green waters) joins Potomac river (seen as a fudge chocolate brown:-))
While Shenandoah is peaceful, calm and crystal clear, Potomac exhibits a vibrancy and rush. When they join and continue on, the river retains its Potomac name, but the intensity is down a notch, the color more subdued and much wider than either.
Kinda seems like how a couple coming together and forming an institution right?