I'm pretty sure it was a gray pool plaster. Gray will render the blueish-green that you see in the image, and as you move more into the sand colored pool plasters, the water will be greener than what we used. I would recommend checking out a few color charts online https://www.google.com/search?source=univ&tbm=isch&q=POOL+PLASTER+COLORS&client=firefox-b-1-d&sa=X&ved=2ahUKEwi8uN-co-TpAhUjO30KHXqiCZoQsAR6BAgGEAE&biw=1536&bih=750&dpr=2.5#imgrc=_mc75Z2tiX_QUM to get a good sense of the range of colors. Hope this helps.

What are the dimensions of this wonderful pool?

15'-6 x 35'-6"