Ishihara 38 Plate Colour Test is the most well known colour blindness test all around the world. It consists of 38 so called Pseudoisochromatic plates, each of them showing either a number or some lines.
According to what you can see and what not, the test gives feedback of the degree of your red-green colour vision deficiency.
This test can only be used to detect red-green colour blindness.
The Ishihara 38 Plate Colour Test is also available in 24 plates, this can be found here.