The Over The Rainbow team discuss the colour yellow. Yellow Ochre was one of the earliest pigments used by mankind. Orpiment was also widely used in antiquity despite it being based on arsenic and being poisonous. Yellow has also long been an important colour culturally. The Greeks - starting from Empedocles - believed that the world consisted of four elements; each of the elements was associated with a colour. Yellow (or a yellow-green colour) was associated with earth; white with air, black with water and red with fire. This tetradic thinking about 4 special colours continued until the 14th or 15th Century; the idea of three special colours is a relatively recent idea. Yellow is probably the least favourite colour and invokes quite different reactions in different people. It is, perhaps, the marmite of colours.

Steve, Helen and Huw tell you everything they know about the colour blue. Feeling blue? Then this podcast is just for you. Early naturally occurring blue pigments were hard to come by. However, ultramarine was a rare exception, made by grinding the mineral lapis lazuli. It was the finest and most expensive blue pigment and was often used symbolically to colour the robes of important people - such as The Virgin Mary - in Renaissance paintings. But where did the phrase feeling blue come from? Perhaps the association started when people noticed that we would turn a little blue in the face if we couldn't breathe. The history of the blue riband event is traced back to Henry VIII and the Order of the Holy Spirit and the knights with their Cordon Bleu. The first new blue pigment in 200 years - YInMn Blue - is discussed. Blue is perhaps the most popular colour in the world; is this because it reminds of things that we like? Blue is a relaxing colour than can help us sleep; but at the same time blue light can keep us awake at night and disturb our sleep. The meanings of blue are many of course; but in the west it is often seen as the colour of trust.

You'll be green with envy if you miss this podcast all about the colour green. Malachite was one of the earliest green pigments and a substantial source was the Great Orme in North Wales (the largest prehistoric mine in the world). Green is also the most dangerous of colours. Scheele's Green may even have killed Napoleon. The team also discuss the association of green with the devil and with Ireland. The use of colour in movies is also discussed and the use of green in The Wizard of Oz is of particular interest. And did you know that the Statue of Liberty was not always green? You do now. But listen to the podcast for the full story.

The Over The Rainbow team kick off The Colour of ... series with red - the colour of love. It was one of the earliest naturally occurring colorants of course; red ochre. Red ochre was used extensively in cave paintings 60,000 years ago or more. These incredible and ancient works of art remain because of the lack of light in these environments. This contrasts with the statues of Ancient Greece and Rome which were gaudily coloured at their time of creation but have faded over the years to the extent that many people mistakenly believed they were designed to be white! Cochineal was another early colorant, made from the crushed bodies of insects but used widely as a food colorant (it is even still used today). Culturally red can mean many things of course and some reasons for these associations are discussed. The historical basis of the term 'red light district' is also explored. On balance, research seems to show that people are viewed as being more attractive if they wear red. Red may be the colour of love, but does t really make the heart beat faster? Research also points to sporting teams that wear red outperforming teams that wear blue. But why is this?

In the last of the series the team discuss colour in fashion are joined by fashionista Caroline. Listen to this podcast if you want to find out why so many top fashion designers use colour in an extravagant way in their designs but personally wear black. Is it because they are afraid of colour? The team briefly discuss David Batchelor's book Chromophobia. The ethics of fast fashion are explored and a future in which people readily buy virtual clothes may be coming. Or maybe we will rent our clothes in the future. The future may be closer than you think. And a great opportunity to see the show out with a snippet from Pretty in Pink by The Psychedelic Furs.

John Dalton was the first person to systematically explore colour blindness (more appropriately called colour deficiency since the vast majority of people with this condition can see colour but have poor colour discrimination. He presented a famous paper - Extraordinary facts about colour vision - in Manchester in the 1790s. We now know that whilst most of us are trichromats (having three types of cones in our retina) some people are dichromats (with only two cone classes) or anomalous trichromats. Recently we have discovered that some people are even tetrachromats and might have exception colour discrimination. This podcast is all about colour blindness.

It's your first day at school and the teacher says 'I'd like you to paint a picture of where you live', so imagines Huw and this begins a dive into the topic of colour mixing. Colour mixing is a widely misunderstood topic. In fact, it is not actually possible to mix colours per se. Colours are perceptions even though it often feels as if they are the properties of objects. What we can do is mix lights and we can mix colorants (dyes or pigments). When we mix lights we refer to it as additive colour mixing and when we mix colorants we refer to it as subtractive colour mixing. Understanding either requires some appreciation about how the cones (light-sensitive cells) in our eyes work. Because the key questions about colour mixing are not about what happens (for example, that red and green lights can mix to make yellow) but about why and even where it happens. This podcast only scratches the surface of this fascinating topic. To dive in deeper you could look at Steve's video about colour primaries.

Does colour and light affect our health and wellbeing? It it really true that red makes the heart beat faster? And what happens to you when you are placed in a pink room? Late-night colour chat. The podcast starts with a discussion about what type of colour vision a unicorn would have if they existed (which they do of course). Eventually the Over The Rainbow team do get on to the effect of colour on health and wellbeing. Does pink make you weaker? Ever heard of drunk-tank pink? And what about colour and heart rate? The idea that red makes the heart beat faster is widespread and assumed to be true; yet the evidence of this is weak at best. On the other hand, light exposure has been shown to be effective as a treatment for seasonal affective disorder. If you like this you might like Steve's piece in The Conversation about the non-visual effect of light on the body. Or, for a deeper dive, consider this review paper.

When did humans first see colour? Trichromacy seems to have been around for at least 30 million years. Our very early ancestors, however, were probably nocturnal and had uv vision. It is thought that about 80 million years ago we developed sensitivity at the longer wavelengths, became dichromats and eventually trichromats. We now know that some humans in fact are tetrachromatic and have four cones. The Over The Rainbow team also discuss the arguments about whether light is actually coloured or whether it just looks coloured. Linguistic relativity and the colour vision of the Himba tribe (Namibia) are also mentioned.

Late-night discussion about the colour vision of dogs, shrimp, bees, cows, bulls and many more. Do dogs see in colour? Are bulls really enraged by the colour red? Does colour even exist? Dogs are dichromats; that means they have two types of light-sensitive cells (cones) in their eye. Most humans are trichromats. We don't really know what it's like for a dog - or any other species - to experience colour. However, we can compare their physiology with ours and we can conduct behavioural experiments. If a dog, for example, can be trained to discriminate between two colours then it tells us something about their colour vision. In fact, most mammals are dichromats including cats and bulls. Bulls have poor colour vision in the red part of the spectrum; it's more likely that the motion of the cape - rather than its colour - attracts their attention.