Swimming pools aren't painted - The color is intrinsic to the Gunite when the pool is made - You have a choice of color when the pool is built or resurfaced.

Here's an online article about how the color of a pool affects the appearance:
http://www.landscape-design-expert.com/gunite.html

thanks for your reply, however in greece they paint swimming pools and I am preparing to plaster my swimming pool (which in greece is plastered with cement - always grey) after that I must choose a colour too paint it, thanks again I will check out your above mentioned site......

Here are lots of color and material options- for plaster interiors.
http://www.nptgonline.com/pool-finishes