Cobalt Blue is a bright middle blue, while Ultramarine Blue is more violet-toned. But Ultramarine Blue also comes in a range of shades, from a Green Shade that is almost identical to Cobalt Blue, to a more violet-toned (and usually more granulating) deep or French shade.
Is Phthalo Blue Red Shade actually red-toned, neutral, or still green-toned but simply less so than its cousin Phthalo Blue Green Shade (PB15:3)? I’ve heard all opinions, and I suppose it’s a judgment call. (Is the color blue you see the same as the color blue I see?) My opinion is that it is a fairly neutral blue without a clear bias toward purple or green. But it’s just as strong and lively as its Phthalo kin.
Phthalocyanine blue (PB15) is an incredibly intense, staining, transparent, non-granulating, lightfast pigment that comes in two versions:
- Phthalo Blue Green Shade (PB15:3)
- Phthalo Blue Red Shade (PB15:6 or PB15:1)
(I’ll call them GS and RS in this post.)
What’s the difference, and which should you choose?
Made from the heavy metal cobalt, this is a true neutral blue that’s neither green-toned nor purple-toned, and is a perfect shade for clear blue skies.