Bob has sent me a photo of a swimming pool and would like to know what the colours of the pastel pencils he should use.
Assuming the Bob is using the Sand Ingres pastel paper we recommend then the first colour should be 101 white generously applied and rubbed well into the pastel paper with your finger or colour shaper.
I would then apply 230 light cool grey then 140 on top of this rub both colours into the white base. Other colours such as 151 and 156 can be introduced as desired using the colour shaper this time so that the colours can be separately introduced where needed.
White and the 230 can also be added to lighten up the lighter areas all the time using the colour shaper not your finger. I have to say that it is not going to be easy to reproduce the effects seen in the photo therefore allowance must be made for this, in other words keep your expectancy low.