Shark Merman Reaching

Hello! I'm from ProjectComment 

First of all, great jobs using references and pose. Despite the anatomical errors, the pose has a really nice flow and clear, line of action. I really like the tail part, it feels so nice to touch and hug for some reason.. 

I'd like to focus on the light. Think of how light travel, simply put ,from the sky, through the water, bounce on the merman. In this case your sea acts like a sunglasses. Imagine if you put on a blue sunglasses and look at the man what will he appeared to be, Bluish man. Your water is the filter for light to pass through. If the water is blue, the light will also be tinted by blue, affecting all the colors illuminated by it. So the colors of the shadow, the skin tones, hairs, etc. will be tinted by blue.

But also not forget, the original colors of light is white and light will looses it's strength by the object it passes through and distance it travel. So the hi-light, the first touch of the light where the light maintain the highest energy, can appear to be white. And the shadow, where the light has weakest energy, will be the most tinted by blue. 
Also the rays of light can remain white as for the aesthetic purpose. Anyway, if you wish to go with Disney's little mermaid style it is fine too! There is no right or wrong. I just purposed the more 'realistic' way of coloring NOT the right way   

Personally I think the sea could be a lot darker. Well, depth is another factor but I just feels it is way to bright. But at least the bottom part of the image has to be a lot darker. 
Just try google, whale, real quick. You will see that even though they are swimming so close to the surface, the water are much darker than yours. Lights fade unbelievably quick underwater, so there is always a huge differences in gradient values from top of the picture to the bottom.

Lighting and colors are tricky. My advice is to also use a references for colors as well not just the pose. 
Hope this help.