PGYS is a highly-staining, highly-transparent, classic grass or emerald green, more yellow than its brother Phthalo Green Blue Shade (PG7).
Experiment Results
Hue: A bold middle to yellow green. Wide range of values from bright to light. The computer made the middle shades look blueish, but they are not in person – it’s evenly yellow-toned all the way down.
Gradient: Nice, even gradient.
Opacity: Very transparent.
Glazing: Extra-dark hunter green glaze.
Color Mixes: Mixes with reds are uninspiring, but Hansa Yellow Light turns into a vibrant spring green, and the blues make nice turquoises. (Phthalo Blue Green Shade + Phthalo Green Yellow Shade is how Daniel Smith makes Phthalo Turquoise!) A pretty, Victorian-looking muted dark green with Quin Purple, and earthy greens with the earth tones. I like the mossy mix with Quin Gold.
Comparison to Other Brands
Winsor & Newton – Winsor Green Yellow Shade
Looks pretty much the same!
Da Vinci – Phthalo Green Yellow Shade
Lightfastness
Extremely slight fading/muting/warming. Not really perceptible in the photo, almost imperceptible in real life.
Comparison with Phthalo Green Blue Shade
Phthalo Green Blue Shade is made from the pigment PG7; the color is cooler/more blue-toned (closer to Viridian, and sometimes Viridian Hue uses this), but similarly wide-ranging in its value range and also highly staining.
Here they are side-by-side:
Color Mixes
Pure Yellow (PY154)
Very vibrant yellow-greens
Nickel Azo Yellow (PY150)
With mostly green, quite a bright color similar to the Pure Yellow mixes; with more NAY, a green gold that reminds me of Rich Green Gold
Alizarin Crimson Quinacridone (PV19)
Not quite complements; dull purples and dark greens
Quin Rose (PV19)
This is quite complementary.
Phthalo Green YS (PG36)
Pretty much a complement, slightly on the cool side of gray.
Phthalo Blue GS (PB15:3)
Glowing teals.
Conclusion
I’m actively in flux on this one. The differences between PG36 and PG7 are extremely subtle, so it’s a totally inconsequential decision, which is what makes it so hard! I have this in my Neon Palette, to make maximally bold yellow-greens, but for my main and Summer palettes, I prefer the cooler PG7.