One effect of colour deficiency is to have a 'dead band' where all colours within a certain range appear the same shade. This can be assessed by using an ordering test similar to the 15 hue test below.

The 15 hue test employs 15 colour swatches covering a range of colour values. The end two are fixed but the rest are initially placed in a random order as above. The patient is asked to re-arrange the swatches into a regular order so that they appear in sequence. A normal colour vision patient will order then as below.

Whereas someone with mild red-green colour deficiency may order them something as below (* marks out of order). The more pronounced the miss-order, then the greater the indicated colour deficiency.

To have a try at this test click here.

A more critical assessment can be made at the expense of simplicity by using a test called the 100 hue test. This is similar to the 15 hue test except that 4 ranges of 25 hues are used. It is very difficult and time consuming to carry out a full assessment with the 100 hue test so the 'colour confusion' tests were designed. The commonest of those is the Ishihara test.