The secret is in the color wavelengths!
Visible light is a combination of light colors; colors are sensations that exist when we fragmented light.
Truth is the ocean does reflect the sky to an extent but it has to be completely calm… yet it’s not the real reason it’s blue.
We see the ocean blue for the same reason we see blue sky (neither is actually blue). Light is a combination of many colors, blue light has shorter wave lengths easier to deflect than any other color. When light enters the atmosphere or the ocean, Oxygen and Nitrogen molecules are not able to scatter much light at long wavelengths. Therefore, they absorb the blue light and bounce the blue around; molecules in the water also do the same. When the water is combined with living creatures they too absorb light and reflect greens, in different depths (more bouncing around) we get darker blues.
At sunset and sunrise, the light must travel through a lot more atmosphere and particles to get to us, and these scatter. Reds have the longest wave lengths and so we get to see them.