The first colour in the spectrum is red whereas violet is the last. For this reason, some people think that red is the warmest and violet is the coldest. However, Helen van Wyk ("Color Mixing", 2000) says that orange is the warmest and blue is the coldest. This coincides with what several artists are saying on the web. For instance, some say that when they want to apply a warm blue, they use ultramarine, because it is warmer than cobalt.
Someone who has reacted against this concept is Sharon L. Hicks (here
). She argues that it derives from a misunderstanding of the colour wheel, which goes from violet back to red, although this transition doesn't exist in reality. Purportedly, it is for this logical
reason that people think that violet is warmer than blue (that is, because violet is adjacent to red).
But she is probably wrong because colour temperature is a subjective property. It does not necessarily coincide with the spectrum. Wikipedia says: "There is historical disagreement about the colors that anchor the polarity [of warm and cold], but 19th-century sources put the peak contrast between red orange and greenish blue" (here
At the fringes of the spectrum artists evaluate that the temperature turns in the other direction. So it is correct that blue is warmer than greenish blue (e.g. cerulean) and red is cooler than red orange (e.g. vermilion). The conclusion is that ultramarine is indeed a warm blue. It is important to know, because the complement of a warm blue is a cold orange. It is also logical, since ultramarine is a violetish blue. We get violet by mixing blue with red. When mixing a warm colour with a cold, it should get warmer than the cold colour. Mats Winther