Pool color

[Sunny France]

I don't have enough money to have a new pool built, but I have a disused concrete water reservoir in my garden 2m wide x 10m long x 2m deep (6ft x 30ft x 6ft deep). On a hot day it looks very welcoming, if only it was filled with water.

Is there a combination of colours, such as light walls and dark floor, or all-white etc, that will make the pool look wider? It's just about wide enough to swim in.