The thing with watercolour pencils is that the colour they have when you apply them as “normal” coloured pencils and the colour they have when you wet the strokes are pretty much differing from each other. That is the reason why I put up a colour swatch for a landscape painting based on the colour “Burnt Siena”.
The first row shows the colour mixes in order to get darker hues (they don’t look as dark on the scan as they do in reality); the second row shows colours you get when you add red and yellow, and the third row shows colours you get when you add strokes of emerald, light green or juniper green to strokes of burnt siena.
Of course the colour mix also depends on the pressure you apply on the pencil. So the colour swatch can only serve as a kind of orientation.