That the Doctor having desir'd him to tell in Order the difference of Colours to his Touch, he did as follows; Black and White are the most Asperous or unequal of all Colours, and so like, that 'tis very hard to distinguish them, but Black is the most Rough of the two, Green is next in Asperity, Gray next to Green in Asperity, Yellow is the fifth in degree of Asperity, Red and Blew are so like, that they are as hard to distinguish as Black and White, but Red is somewhat more Asperous than Blew, so that Red has the sixth place, and Blew the seventh in Asperity.
"Experiments and Considerations Touching Colours (1664)"
Robert Boyle