The test consists of a series of images, showing many circles of different sizes and colours.
Each image could have painted circles forming a shape of a one to two-digit number.
If you are unsure about the number, type in your best guess. You can also skip the answer, if you don't see any number.
This test is an approximation of colour blindness.
It's not a definitive answer, because it depends on screens displaying colours differently and some other factors.
However, you can use it to get a good approximation.