Full Idea
By the different structure of our organs the same object could produce in several men's minds different ideas, viz. if the idea that a violet produced in one man's mind by his eyes were the same that a marigold produced in another man's.
Gist of Idea
The same object might produce violet in one mind and marigold in another
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.32.15)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.389
A Reaction
This is Locke's original proposal that inverted qualia might be possible, but note that he proposes a physical basis for the inversion, in 'different structures'. Without that, claiming qualia inversion is the same as claiming that zombies are possible.