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)
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.
Book Reference
Kant,Immanuel: 'Prolegomena to Any Future Metaphysic', ed/tr. Lucas,Peter G. [Manchester UP 1971], p.46