What chart is used for color vision acuity?

Color vision tests are done with charts that have one big circle made up of tiny dots of one certain color and within that circle there are dots of another color that make up a number. The colors of the dots vary from chart to chart and so do the numbers and letter.

To test whether your color blind your shown a series of charts and asked what number you see. If you cant make a distinction between the colors then you wont be able to see the number that the different colored dots make up within the circle, therefore being color blind. If you can see the number then your good.