YELLOWNESS INDEX (ASTM E 313)

Yellowness Index is a number calculated from spectrophotometric data that describes the change in colour of a test sample from colourless through to yellow.

The American Standards Test Methods (ASTM) has defined whiteness and yellowness indices. The ASTM's E313 yellowness index is used to determine the degree to which a sample's colour shifts away from an ideal white. The D1925 yellowness index is used for measuring plastics.