Oh my gosh so sexy! Well let's take a look here. First off I love this version over the plan white background version, and I haven't seen the "blue version" but I do like this one. I would be interested to seeing this with a very light blue background but this probably was the better choice in the end.

With such a dark skin tone it is difficult to show off shadows. At some points it would be better to add some more lighter shades to the light areas of her body. Just a bit more so that the definition of the character can come out.

Her feet are a bit wonky, the sole of the foot should be turned more up so that her butt is sitting right on the heel. That's how you normally sit on your heels when you drop to your kneels. And the back arm might be a bit off but it's rather well done. This is a difficult pose and with difficult color tones you pulled it off surprisingly well. She just looks so damn hot!

I love the use of colors here, and your texture of the sand is fantastic! Other then a few small anatomy things this is almost perfect in every way! Very well done in my opinion.