White created by light on a TV screen, for example, or through a prism, does not have its own specific wavelength. Rather, it is the sum of all the colours. Think of a rainbow: you can't see the colours of sunlight except when raindrops refract the light rays and reveal the whole spectrum. Because of this, scientists do not generally count white as a colour.
However, in your day-to-day life, you can go to any DIY shop and see endless shades of white huddling together in the paint section. So when it comes to pigment, rather than light, white is most definitely a colour.
In prehistoric times, our ancestors used white chalk to create their art. Readily available, chalk is a kind of limestone made of the mineral calcite, which can be crushed easily to create not just cave paintings, but giant artworks, such as Uffington's white horse or the Cerne Abbas giant.
In written records, the earliest mention of a white pigment that is not plain chalk comes from the Italian artist Cennino Cennini in the 13th century. He used the term Bianco di San Giovanni to describe a white lime pigment made of calcium carbonate and calcium hydroxide. Artists dried out lime, then reduced it to a white powder that was immersed in water for eight days, with the water changed each day. It was then made into small cakes that were left to dry in the sun.
The other way to make white was to use lead. The process was described by Pliny the Elder: pieces of lead were put into clay pots that had a separate compartment filled with vinegar. These were piled on shelves next to cow dung. Over a month or so, the fumes coming from the vinegar and the cow dung caused the lead to corrode into lead carbonate, a beautiful white compound that was, unfortunately, pretty toxic. Lead white was actually the only white used in European paintings until the 19th century, when its manufacture was finally restricted. Now, in the EU, lead paint can now only be used for the restoration of works of art and historical buildings.
For much of human history, white has been a symbol of purity. It was worn by priestesses in ancient Egypt and Rome, while ancient temples were faced with white marble. The Pope has worn white since 1566, as a symbol of purity and sacrifice, and it is worn by pilgrims in Islam and the Shinto religion of Japan.
We all think of white as having a place at weddings - the white dress worn by brides symbolises virginal innocence and new beginnings. Interestingly, white used to be reserved solely for royal weddings - non-royals just wore their Sunday best - up until the 19th century, when Queen Victoria's lace wedding dress inspired a fashion for white.
White is also the colour most associated with cleanliness. Laundry powders promise to get your clothes 'whiter than white' because white means clean. Refrigerators and dishes, toilets and sinks, bed linen and towels are all traditionally white. White was the traditional colour of the coats worn by doctors, nurses, scientists and laboratory technicians, and it's often worn by chefs, bakers and butchers.
White is best for a fresh start. It's a blank canvas, it's a new page. Start with white and you'll be all right (unless you're applying makeup, that is).