Yellow-Red and Blue-Red
822.
These, when placed together, as the deepened extremes of both sides, have something exciting, elevated: they give us a presentiment of red, which in physical experiments is produced by their union.
823.
These four combinations have also the common quality of producing the intermediate colour of our colorific circle by their union, a union which actually takes place if they are opposed to each other in small quantities and seen from a distance. A surface covered with narrow blue and yellow stripes appears green at a certain distance.
824.
If, again, the eye sees blue and yellow next each other, it finds itself in a peculiar disposition to produce green without accomplishing it, while it neither experiences a satisfactory sensation in contemplating the detached colours, nor an impression of completeness in the two.
825.
Thus it will be seen that it was not without reason we called these combinations characteristic; the more so, since the character of each combination must have a relation to that of the single colours of which it consists.