In the IR+HRV RGB, the ocean surface is depicted in black. Short wave solar radiation is absorbed by the water surface. IR10.8 does not contribute with the blue colour beam as the sea surface is rather warm.
In summer time, the ocean surface appears more bluish (see image below). This is due to the higher elevation of the sun. Short wave radiation is more absorbed and less reflected from the water surface at high angles. Though being relatively warm, still the IR10.8 component (blue) dominates over red and green from HRV.