The colour of water is determined by:
A) What’s under it.
B) What’s in it.
C) What’s on it.
D) And by light levels and angles, including the colour of the sky.
In this picture, taken from Climping Beach in West Sussex, we can see a good example of all four.
A & B) The sea is beige where we can see the sand beneath the water and also where the waves have churned up the sand.
C) It is white where foam bubbles rest on it.
D) It is lighter where the sun is hitting the water and darker where there are cloud shadows. If you look beyond the browns and beige colours, you’ll notice the water goes from light blue/green to dark blue/green and then back again. The dark patch in the middle is a cloud shadow.
For more detail, see the ‘The Colour of Water’ chapter of How to Read Water.