With RTV Paint you can select predefined colours from the various manufacturers colour book files or you can use the Colour Picker to select your own user defined colour from the colour wheel.
The paint manufacturers colour book files must reside in the Colourbook folder location you define from the settings menu in order for them to be displayed in the Colourbook library drop down selector.
To select a pre-defined colour launch the RTV Paint plug-in.
From the Colourbook Library drop down selector chose a manufacturers colourbook. If you know the name of a colour in the selected range you can type it in the Search Filter window making it easier to locate it otherwise you can scroll through the list of available colours in the selected range to find the colour required and click on it to select it.
Depending on the colour selected and the Colour book selected you may also see additional Similar Colours and Complimentary Colours displayed which can then be loaded into your Revit project.