This colour vision test, known as the Ishihara Test, creates numbers out of dots that are a different colour to the surrounding dots. A person who is colour blind, sees all of these dots as the same colour, whereas a person with normal vision, can distinguish the different colours.
The Colour Blind Test or the Ishihara Test contains a number of coloured plates, known as Ishihara plates. All of the plates contain a circle of dots appearing in random order of colour and size. Most people will view the images differently (mostly Arabic numbers). Those with certain types of colour blindness will see different numbers from those not affected by colour blindness.