Water isn't colorless, it is actually blue. The deep clear water is always blue but other things in it give it different color. To have blue water you need water of low turbidity and low fertility and it help to a have a bottom that reflects the full spectrum of visible light (eg a white sand or limestone).

Don't know if you plan to have fish in this BOW but feeding them will turn what might otherwise be blue water to green ... something a fisherman doesn't mind seeing.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers