This actually exists and it’s a colour measurement instrument, invented 225 years ago. It is called cyanometer and it was designed to measure the blueness of the sky. This 18th century circular device is composed of an array of 53 shades of blue. Swiss physicist Horace-Bénédict de Saussure and German naturalist Alexander von Humboldt  started using it in in 1789 in their experiments to calculate the amount of water vapor in the atmosphere though the transparency of the sky.