Full Idea
Ideas such as those of colour and pain are not arbitrary. ...That is not God's way ...I would say there is a resemblance of a kind, not a perfect one, but a resemblance in which one thing expresses another through some orderly relationship between them.
Gist of Idea
Colour and pain must express the nature of their stimuli, without exact resemblance
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 2.08)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.131
A Reaction
The main point of Locke's idea of 'secondary' qualities is that (unlike the 'primary' ones) they bear no resemblance to their stimuli. It's not much of an argument from Leibniz, to say that is not God's way, but he has a vast system to support his claim.