Quite a few prominent people studied rainbows. Aristostle, the Greek philosopher, noticed how colours can look different in front of different coloured backgrounds, and he tried to develop a standard for what the main colours of the rainbow should be. At first, he said that there are seven main colours that could be mixed to create the visible spectrum of colour. Those seven colours were white, yellow, "phoenician", violet, green, deep blue, and black. But when Aristotle wrote about rainbows, he changed that standard to just three colours. Those three colours were red, green, and purple.