Oceans, lakes and rivers appear dark blue in the HRV Cloud RGB images.
Water acts almost as black body for short wave solar radiation, hence the albedo is near zero and there is no contribution from the red and green colour beam.
The blue colour beam reflects the water temperature. Water not covered by ice contributes only little with blue colour, but since the red and the green contribution are almost zero, the overall colour hue is dark blue.
HRV Cloud RGB from 21 July 2015, 12:00 UTC
Explanation of the dark blue colour of oceans, lakes and rivers in the HRV Cloud RGB (see the recipe):
• As the albedo of water is near zero, only the blue colour from the IR10.8 channel contributes to the HRV Cloud RGB. The blue contribution is very small.