You'd have to know what pigments he used, in other words, what ingredients he used to make different colors of paint, because the ingredients used in paints and binding agents have changed over time.

你要知道他使用了什么颜料，换句话说，他用了什么原料来制造不同颜色的油漆，因为油漆中使用的原料和结合剂都随着时间的推移而改变。