There are a couple of small applications that make it a lot easier to capture the colours you want to use in your render.
The first is Faststone Capture this lets you grab a section of the screen and save it to disk. This can be used to capture colour pallets that you can then use in conjunction with ColorCop. This has an eye dropper tool that can capture around 8 separate colours from any whereon the screen.
Using these tools in combination you can capture a pallet or any other area of colour with FastStone and then use ColorCop to capture the individual RGB values.
ColorCop will stay on top of other running applications so that it is visible whilst using Photoworks so you can copy the RGB values into the Photoworks pallet. This is a great time saver and very accurate, just a pity Photoworks doesn’t have its own Eye dropper tool, but then that would be too easy.
ColorCop shown here sitting on top of the Photoworks screen adjacent to the colour pallet with the RGB values shown.
Solid Impression 
This is a great post with a great solution. PhotoWorks should really incorporate something like that, although it’s nice to have a separate program to use with other programs like photoshop.