Colour mixing in watercolour
It is also worth noting that Burnt Sienna and Winsor Blue [Green shade] mix together make a nice dark green, a number 6 in a tone (or value) chart.
The colour theory bit – Winsor Lemon and Winsor Blue [green shade] (being as near pure primary colours as I can find) make the brightest greens as they are both cool primary colours with no hint of red in them. By adding red to a bright green made using these two cool colours (Winsor Lemon and Winsor Blue [green shade]) the green will have all three primary colours in it, making it neutral (not bright).
On the other hand, both French Ultramarine (a warm blue) and Raw Sienna (a warm yellow) already have red in their mix - look at your colour wheel for their placement – the colour of Raw Sienna can be mixed using Winsor Lemon and a touch of Permanent Rose, and French Ultramarine is placed towards the violet side of the wheel as this too has some red in it. So, these colours (Raw Sienna and French Ultramarine) are not pure primary colours (they are a mixture of two primary colours) which is why, when they are mixed together, they cannot make a bright secondary green (they make neutral grey-greens).
Because of this we often find adding one cool primary to one warm “primary” makes more natural (muted greens). For example:-
Winsor Lemon (cool) and French Ultramarine (warm)
Raw Sienna (warm) and Winsor Blue [GS] (cool)
Burnt Sienna (warm) and Winsor Blue [GS] (cool)
Adding a small amount of red is particularly useful with ready made bright green paints, Viridian and Hookers Green, for example. Sap Green already has some red in the mix making it a more natural green although since I can mix this colour easily I do not include it in my limited palette of 6 colours.
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