ISO 6271:2015规定了以铂钴单位（Pt-Co单位）估算透明液体颜色的分光光度法。它适用于颜色特性与附录a中规定的铂钴色标相似的透明液体。对于颜色比铂钴储备溶液更浓的产品，ISO 4630中规定的方法适用。 分光光度法提供了一种比肉眼目测样品比较更精确的测量铂钴颜色的方法。 注:此处使用的术语“Pt Co颜色”优于术语“黑森颜色”和“APHA颜色”。

ISO 6271:2015 specifies a spectrophotometric method for estimating the colour of clear liquids in terms of platinum-cobalt units (Pt-Co units). It is applicable to clear liquids having a colour characteristic similar to those of the platinum-cobalt colour scale specified in Annex A. For products with colours more intense than the Pt-Co stock solution the method specified in ISO 4630 applies. The spectrophotometric method provides a more precise way of measuring Pt-Co colour than a visual sample comparison by human eyes. NOTE The term "Pt-Co colour" used here is preferred over the terms "Hazen colour" and "APHA colour".