Had an email the other day from Lisa Marder, I think the name is .... she provides links to various arty blogs and comments on them herself. The gist of this one is that blue, which is normally considered a cold, recessive colour, can be warm - and goes on to say that Pthalo Blue can be a warm blue (whereas most of us might consider it one of the coldest blues you can get). All I think this does is point up the very vague words sometimes used by artists - while ignoring some basic science. Warm and cool are actually fairly meaningless words in artistic terms, because of course they refer to no actual physical property at all. Probably we do divide our palettes and painting practice into warm and cool colours, but what we mean by that is that we know some colours come forward in a painting, while others recede in relation to them. It's a nonsense therefore to ascribe temperature to a colour on its own - it's how it works with the rest that's important. From a practical point of view, I've long considered Ultramarine the only warm blue, because it leans towards purple - it contains red, in other words. The rest, Pthalo, Prussian, Cobalt, Cerulean/Coeruleum, and a good few others, are by comparison cool - they convey in some cases a sense of distance. I say in some cases, because they don't all do that: Prussian and Pthalo Blue are so intense that they can certainly come forward, and dominate a painting. But does this make them "warm"? You wouldn't use them for the distance, unless they were extremely reduced in hue; personally, I would hesitate before using them even then - Cobalt and Cerulean blues, mixed with a little red, are more useful in landscape for indicating far away features. Desaturating an already gentle colour is much easier than trying to desaturate a powerful screamer like Pthalo Blue ... Distant objects are partially obscured and distorted, in most weather conditions, by the atmosphere between us and them (there are days in which a distant field of rape can still hit you bang in the eye, and every detail is sharply defined: we don't get many of those). That atmosphere can be conveyed in various ways, but as it has blue in it, a blue, grey, or even purple hue tends to describe it best. Look up at that thing called the sky, and you'll readily understand why blue is used to represent distance - it IS the atmosphere. So I think in this argument that already nebulous words have been taken too literally, and as if they had more substance that they do. Warm and cool as a means of dividing colour only works in very general terms anyway - where do the greens fit, for instance? - but a painting that is predominantly blue is going to look "cool/cold" whatever you do; that's going to be less true if the blue used is Ultramarine, or even Pthalo Blue Red Shade, but it's still going to be perceived as colder than a painting employing primarily Burnt Sienna, Umber, Ochre, and the bright reds and richer yellows. Does it matter? Only I think in the sense that it confuses an already rather woolly subject - for me, relative warmth is conveyed by there being a detectable amount of red in a given pigment, and relative coolness by its absence - which means of course that some very bright greens, eg mixes of Pthalo Blue and Lemon Yellow, are still going to be cool. In practice, I find this a lot easier than getting too hung up on attributing temperature to colours. although it might be useful in reminding us that this is just an artistic convention anyway, and like most things, including the Gospel, it shouldn't be taken as the Gospel.