I don’t believe there is such a thing.
I think of colour as light, so black would be the complete absence of it. Light is simply various frequencies of the electromagnetic spectrum and we can’t see much of that spectrum. When artists talk about ‘pure colour’ they are usually talking about a specific pigment and many natural pigments can reflect a very narrow band or bands of the electromagnetic spectrum.
Don’t get confused about this because I don’t think it maters much to most artists, at least it doesn’t mater much to me; the only reason I’m talking about it is that I’ve heard the term used seriously incorrectly by several artists. This post was written because I read an article where the term was used and it was used as if it meant something specific and technical. I’ve noticed that many very technically minded people have very low opinions of artists, who don’t understand some of the more technical aspects of the world around us but I feel those technically minded people are sometimes blind to the beauty around us. I’m often reminded of a lady I met in university who saw colours in mathematics. She saw equations, and numbers, as colours and manipulated them accordingly. I asked her about a red sign and she called it ‘empty’ she liked green because it was ‘fuller’. I was often jealous of what she saw because she described it beautifully.
I don’t pretend to understand what she was seeing and I understand that it is explained as a crossing of connections in our brains associated with the visual cortex. It even has a name, Synesthesia. But it makes me wonder what we would see, and what our art would look like, if we had the eyesight and visual system of the Mantis Shrimp.
So, if I were going to give advise, I would advise to ignore anything that used the term ‘pure colour’ and concentrate on what you see. Our vision, as imperfect as it is, is still the method used to view art so it is the best tool we have to create it.