Searching for a nice watercolor blue to paint my California sky

[Guest Post by Delphine Doreau in Los Angeles] For a long time I was very comfortable with gray. Blue, and especially blue skies, was a luxury in Paris or San Francisco where I lived, something joyful to experience with delight…and rarely sketch. Blue was out of my comfort zone as a sketcher. And then, I moved to LA seven years ago. Here, the sky is blue, a blinding, glorious and lovely blue, most of the time. When I decided to seriously learn to paint watercolor sketches, I had to handle it…and realized I had never given it a real thought.

Painting a beautiful blue sky in watercolor sounds very straightforward, but it’s actually a difficult task. There’s the whole thing about gradients and paper and dilution of course, but this can be solved with a little exercise and some very good paper.

The biggest problem is actually color. We, as humans, have a good notion of a medium blue. I looked up for a medium blue of 475 nanometers, and found it to be quite unsettling: it’s exactly as I imagined it. We all have different versions of basic colors, our own cultural and personal palettes. It’s normally impossible to imagine a universal, medium color. It’s difficult to define red, some see it more tomato, others more carmine. Yellows are even more difficult and green–don’t even think about it. But blue, we have a good notion. It is quite interesting if you think about it. Is it because of the very little occurrence of that color in nature apart from the sky?

Blue sky tests at the Huntington Gardens, in San Marino, CA. This was before I understood that I really, really needed to wet my paper before painting skies.

If you want to sketch a clear blue sky you know what you want to show, wouldn’t it be nice to have the exact right blue (or blues) in your palette? 

Problem: There’s not so many blue pigments.

And even if you can get the right hue, the right saturation and values are hard to find if not impossible. The sky, pure blue sky, is blue because of Rayleigh scattering: particles in the atmosphere scattering the blue light more than red. It’s the light of the sun, scattered. It’s more luminous than paper, more luminous than any paint.

I made tests: Prussian blue is too dark, Phthalo is too green and too intense, Ultramarine is nice as a touch but a bit too dark and purple…this, for the not obviously, classic historical pigments that are lightfast and easy to find. I tend to prefer non toxic pigments or not too toxic paints because my cat loves to drink my paint water. I also look for paints with only one pigments at first when building my palette. For example, I quite like Verditer Blue from Daniel Smith, but it’s made of three pigments including a gouache-like white, a lovely color but probably not the best building block for a restricted palette. So I continued my search for nice paint made from possibly only one pigment with a historical background…

Some sky tests

I couldn’t find a nice blue for my Californian sky. It was very disappointing. I made some research for grays and discovered that cobalt made some delightful cold grays mixed with raw sienna. I tested it but then hesitated. What a beautiful blue.

I looked around for solutions. Richard Parkes Bonington has some beautiful blue skies. John Sell Cotman, too, has delightful, intense blues. So I looked up what kind of paints they had access to in their time. It could be ultramarine, prussian blue…or it could be cobalt. It made me go back to this pigment.

I had some cobalt tucked away, two small tubes, from Sennelier, and Winsor & Newton. Both are the same pigment composition, PB 28, but unlike phthalo green or some other colors that are fairly consistent through the spectrum of brands, I was surprised to discover that the Sennelier cobalt was more ultramarine (reddish) than the Winsor & Newton. It doesn’t show much after scanning a RVB picture, but in reality the difference is more visible. Both are beautiful and intense and will make deep saturated skies, combined with other colors for depth. Cobalt blue turns to lovely grays once adding a touch of light red (PR102) or raw sienna, which makes creating clouds a real fun task. So it makes it a very lovely addition to a small, summer sketching palette.

And doing more research, I found out that the closest pigment to that magical medium blue is coeruleum (Which translates roughly in Latin to “ the color of the sky or the sea”).

Cerulean blue is a good color, and something the great painters of the 19th century had access to. But a real one (PB 35) is difficult to find. I bought a Daler Rowney one.

It’s almost the right thing for a French sky, a nice, medium blue with a beautiful granulation, but not quite as intense as one would like. There’s a hint of green in it, that you can find in some skies, but it’s not as intense as cobalt. This said, it’s a lovely color to add to a palette, as it makes lovely mixes with other colors.

So…I’m ready to change my palette, again!

Delphine is a French artist living in the Hollywood Riviera in Los Angeles. She’s an Art Director and blogs her work at


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