to add to what warren is saying; if you add enough pigment it will work but the base colour is white so keep in mind that if you don't add enough red for example you'll end up with a pink part  
if you'r looking for translucent coloured parts you'r better of with the glasscast products...only downside is longer curing

Thanks Warren and Matthieu for the info. I was trying to decide how to colour some small switch control knobs for an old car. The nearest colour in the standard polyurethane pigments is Ivory but supplied in 500g (which is a lot when mixing at 10% in small amounts of resin). The translucent colours are apparently in smaller, liquid amounts and mixable but it was not obvious in the product details that they were suitable for P2 because they were advertised for Water Clear Resin. As I am experimenting on behalf of a classic car club it was decided that trying to mix tiny droplets of colour to obtain a resemblance to ageing would be difficult to control.  Therefore the decision was made to opt for the Ivory Polyurethane pigment whereby we could mix a percentage of pigment in Part 1 of the resin in a larger amount which would maintain a consistent colour when mixing with Part 2.  For example: our components only require very small amounts of resin which makes adding 5 or 10% of pigment difficult to measure and control. By mixing say 100mg of Part 1 with 10% of pigment we would be able to make a complete set of control knobs of the same colour when mixed with Part 2.   
Thanks again for your help. It's nice to know that there are people out there willing to help a beginner/amateur.  Chris.