Blues: Warm and Cool with Watercolor
Just like with yellows, the "warmth" or "coolness" of a blue depends on which way it leans on the color wheel. Since blue sits between green and violet:
Warm Blues lean toward Violet/Red.
Cool Blues lean toward Green.
1. Warm Blues (Red-Leaning)
These blues have a tiny hint of red in them, which makes them feel "heavier" and deeper. They are the best choice for mixing beautiful, moody purples and violets. However, because they contain a trace of red (the opposite of green), they can make your mixed greens look a bit "earthy" or muted.
Common Names: French Ultramarine (on your list!), Ultramarine Blue, Cobalt Blue (though it’s often considered a "true" or middle blue, it leans slightly warm compared to others).
Best For: Deep shadows, night skies, and mixing purples.
2. Cool Blues (Green-Leaning)
These blues have a tiny hint of yellow/green in them. They feel "icy" and bright. Because they already lean toward green, they make the most vibrant, electric greens when mixed with yellow. If you mix them with red, that tiny bit of green can make your purples look a bit grayish or "muddy."
Common Names: Phthalo Blue (the blue version of your Phthalo Green), Cerulean Blue (on your list!), Prussian Blue, Manganese Blue.
Best For: Sunny skies, tropical water, and bright spring foliage.
Looking at Your Palette...
You have an excellent selection to play with:
French Ultramarine is your classic Warm Blue.
Cerulean Blue is your classic Cool Blue.
Lynnie