Full Idea
I can make little sense of the assertion that the sensation of red is similar to the property of the vermilion [cinnabar] which excites this sensation in me.
Gist of Idea
I can make no sense of the red experience being similar to the quality in the object
Source
Immanuel Kant (Prolegomena to Any Future Metaphysic [1781], 290)
Book Reference
Kant,Immanuel: 'Prolegomena to Any Future Metaphysic', ed/tr. Lucas,Peter G. [Manchester UP 1971], p.46
A Reaction
A sensible remark. In Kant's case it is probably a part of his scepticism that his intuitions reveal anything directly about reality. Locke seems to have thought (reasonably enough) that the experience contains some sort of valid information.