I paint a lot of skies, especially sunset skies. A blue-to-yellow gradient in the sky is super common at sunrise, sunset, and golden hour. One of my favorite “colors” in nature is that pale, strange, blue-and-yellow-at-the-same-time kind of color you get in the sky as the blue zenith fades to the golden horizon. Naturally, that’s tricky to get in paint, where blue + yellow = green. Unless there’s a very unusual weather effect, green is an uncommon sky color! So what colors can you use to paint a blue-to-yellow gradient in watercolor without getting green in your sky?
Choice of Yellow
To show how your choice of yellow affects the ease of painting a non-green sky, I’ll pair each yellow with Phthalo Blue Green Shade, a blue that’s very prone to go green. In general, bright, primary yellows are most prone to go green, while more muted, earthy yellows are less greenable.
Most Difficult: Middle Yellows
The typical primary yellows you find a limited palette are great for mixing green, but that’s exactly why you don’t want them in skies.
Plus, they’re so bright that I find them a little, I dunno, garish-looking in the sky.
Still Pretty Difficult: Heavy Metal Complex Yellows
Heavy metal complex yellows, like Nickel Azo Yellow (PY150) and Rich Green Gold (PY129), are also very green-mixing, though I found PY150 pleasantly glowing in dilute. Actually, I was pleasantly surprised with this swatch. A little green in the sky is okay.
Note that Quin Gold, which is made from PY150, still mixes green just about as readily, even though it also contains an earth orange component that somewhat modulates it and makes it look browner.
Still Fairly Difficult: Orange-Yellows
Orange yellows are going to mix less bright greens than bold yellows. You might find the greens they mix tend more toward brown and less toward lime green. But I don’t find they resist mixing green, really. In fact, many companies use orange yellows like PY65 and PY110 to make their Hooker’s Green mixes.
Easier: Yellow Ochre (PY42, PY43)
The yellows that mix green the least will be those made from earth pigments. PY42/PY43, the yellow ochre pigments, are moderate green mixers.
Even if your earth yellow looks muted compared to your bright yellow when you look at swatches side-by-side, you will find that many earth yellows still “read” as bright yellow in the sky when they are diluted and when they are the yellowest thing on the page.
That said, while it doesn’t easily go green, Yellow Ochre can be tricky just because it tends to be quite strong and opaque, which means it’s easy to go too strong, dull, and brownish. You can see in my example above that the yellow in the gradient is a little too heavy-handed, and I only achieved the “glowing” diluted yellow in the sample at the bottom right.
A yellowish Raw Sienna made from PY42, such as Winsor Newton’s, may be easier because they tend to be more transparent and weaker.
Easy: MANS/Yellowish Brown (PBr7)
Earth yellow made from PBr7, a brown pigment, can resist green even better than PY42. On the negative side, it can look too dull and brown for skies, depending on the formulation. I like Monte Amiata Natural Sienna, pictured, because it’s made from PBr7 but it looks quite yellow in dilute. It’s granulating, but looks smooth in dilute, and doesn’t rush to mix with other pigments: it tends to stay where you put it.
Take care, though; PBr7 is one of those pigments that can have many different hues, including dark brown (such as in Burnt Umber or Raw Umber).
Even PBr7 paints called Raw Sienna are mostly more on the brown or orange side, which may not look right in the sky. For example, I find Da Vinci’s orange/brown leaning Raw Sienna never quite looks yellow enough, even in dilute. It’s a great color for dirt and sandstone but not so much for skies.
My Favorite: Naples Yellow Deep (PBr24)
My not-so-secret weapon is Naples Yellow Deep (PBr24), which looks very buttery yellow on the page but is made from a brown pigment that resists greenification (unless you mix it vigorously). This is probably my favorite sunrise/sunset pigment. It is opaque and can look heavy and brownish-orange in masstone, but has a glowing orange-yellow color in dilute, and its range of acceptable values is wider than that of Yellow Ochre.
Choice of Blue
Because there are fewer blues to choose from, I’ll discuss specific pigments instead of subcategories. In general, green-leaning blues turn green easiest (such as cyan), while violet-leaning blues avoid turning green. In my examples, I paired them all with Nickel Azo Yellow.
Most Difficult: Prussian Blue (PB27)
Prussian Blue (PB27) is a cyan/dark blue which longs to go green. It loves to make green.
Still Pretty Difficult: Phthalo Blue (PB15)
Phthalo Blue Green Shade is also a cyan. We saw this above, since I used it as my test blue in the yellow section. Here it is again.
Its cousin Phthalo Blue Red Shade will be easier.
The unmixed color of Phthalo Blue RS looks much more middle blue, less cyan, but the two Phthalo Blues really mix pretty similarly.
Moderate: Indanthrone Blue (PB60)
My Indanthrone Blue (PB60), from Daniel Smith, is among the more violet-toned options for this pigment. Other PB60’s, like those from Da Vinci and WN, have greener colors and are more prone to mix green.
Easier: Cobalt Blue (PB28)
Cobalt Blue (PB28) looks to me like a fairly balanced, middle blue, neither particularly green-toned nor particularly violet-toned. Although unmixed it most resembles one of the more difficult colors, Phthalo Blue RS, I actually find it mixes much more like a violet blue, similar to Ultramarine Blue, below.
Easiest: Ultramarine Blue (PB29)
Ultramarine Blue (PB29) is a staunch violet blue, which makes it the least ready to mix green. It is also a very well-behaved pigment that tends to stay where you put it, not necessarily rushing to mix with any water it touches.
Below I used French Ultramarine, an even redder-leaning and more granulating version, in a light diluted wash.
Mixed Colors
Although I used unmixed colors in my examples above, in reality, I often use mixed colors in skies, such as a modulating a greenish blue with pink or red to make it more violet-toned, or mixing multiple blues to get a color in-between. The caveat here is that if you use any green-mixing paints in your mixes, you’ll still risk getting green where the yellow and blue touch.
I particularly advise using mixed blues, since the blues I see in the sky are more muted than most unmixed colors. I also advise keeping the mix lighter-valued (more diluted) than I have shown in most of my examples. In this type of golden hour/sunset/dusk sky, where blue fades to yellow, I find I often underestimate how low-chroma and how light-valued the blue should be.
Here are some swatches where I was really trying to mix the colors I saw outside the window.
Conclusion
I use various blues and mixes for the sky, but in most cases since 2023, when you see one of my blue-to-yellow sky composition paintings, the yellow is Naples Yellow Deep.
You don’t have to choose NYD, but if you want to avoid green in skies, I think the best move is to use an earth yellow.
I stress the choice of yellow instead of the choice of blue because:
- Different blues give very different artistic effects. For me, the downside of always using violet-blue is not worth the loss of options: I’m not willing to give up cyan.
- The choice of yellow has less of an effect on the overall scene. A wide range of yellows “read” as horizon gold yellow in the sky, especially when diluted.
- I often find my sky’s yellow horizon glow looks more convincing when I use a muted yellow anyway!
While I think using an earth yellow is the easiest way to avoid green in the sky, choice of paint isn’t the only factor. You can get away with using any paints you wish if you use the right technique. I’ll cover that in a future post!
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