The perception of yellow in bruises.

For forensic purposes, the presence of the colour yellow in a bruise may be regarded as indicating it is not recent. However, a previous study has shown that observers may disagree in their description of the colours in a bruise. This study was designed to determine how consistent observers are in perceiving the presence of yellow. Subjects were shown a series of photographs of a bruise that had been digitally modified (Adobe Photoshop) to contain amounts of yellow that increased from 2% to 20%. The point at which subjects first perceived the colour yellow was recorded. The perception threshold for yellow ranged from 4% to 16% (mean=8.7%, median=8%) in the 50 subjects that had normal colour vision. Statistical analysis indicated that an individual's yellow perception threshold increased by 0.07% each year, but gender had no effect. The results reveal that there is variability in the perception threshold for yellow in the general population and that a subject's ability to perceive yellow in a bruise declines with age.