Colour vision test cards provide a quick and easy way to test for colour vision deficiencies. For the cards to be effective, the colours have to be printed with reasonably accuracy and not allowed to fade. This monitor is unlikely to display the colours accurately in the coloured illustration, but you should be able to see how the card works.
The number on the card is distinguished by its hue. It will only be visible to someone whose eyes can see the difference between the blue-green and orange-red hues. The differences in luminance of the coloured dots provides no information about the digits on the card—as you can see from the greyscale illustration of the same card.