The shadow of _q r_ at _o p_ is red, being caused by the blue light _d e_; and the shadow of _q r_ at _o' p'_ is blue being caused by the red light _a b_. Hence we say that the blue light in this instance causes a red derived shadow from the opaque body _q' r'_, while the red light causes the same body to cast a blue derived shadow; but the primary shadow [on the dark side of the body itself] is not of either of those hues, but a mixture of red and blue. The derived shadows will be equal in depth if they are produced by lights of equal strength and at an equal distance; this is proved. [Footnote 53: The text is unfinished in the original.] [Footnote: In the original diagram Leonardo has written within the circle _q r corpo obroso_ (body in shadow); at the spot marked _A, luminoso azzurro_ (blue luminous body); at _B, luminoso rosso_ (red luminous body). At _E_ we read _ombra azzurra_ (blue tinted shadow) and at _D ombra rossa_ (red tinted shadow).] On the nature of colours (277. 278). 277. No white or black is transparent. 278. OF PAINTING. [Footnote 2: See Footnote 3] Since white is not a colour but the neutral recipient of every colour [Footnote 3: _il bianco non e colore ma e inpotentia ricettiva d'ogni colore_ (white is not a colour, but the neutral recipient of every colour). LEON BATT. ALBERTI "_Della pittura_" libro I, asserts on the contrary: "_Il bianco e'l nero non sono veri colori, ma sono alteratione delli altri colori_" (ed. JANITSCHEK, p. 67; Vienna 1877).], when it is seen in the open air and high up, all its shadows are bluish; and this is caused, according to the 4th [prop.], which says: the surface of every opaque body assumes the hue of the surrounding objects. Now this white [body] being deprived of the light of the sun by the interposition of some body between the sun and itself, all that portion of it which is exposed to the sun and atmosphere assumes the colour of the sun and atmosphere; the side on which the sun does not fall remains in shadow and assumes the hue of the atmosphere. And if this white object did not reflect the green of the fields all the way to the horizon nor get the brightness of the horizon itself, it would certainly appear simply of the same hue as the atmosphere. On gradations in the depth of colours (279. 280). 279. Since black, when painted next to white, looks no blacker than when next to black; and white when next to black looks no whiter than white, as is seen by the images transmitted through a small hole or by the edges of any opaque screen ... 280. OF COLOURS. Of several colours, all equally white, that will look whitest which is against the darkest background. And black will look intensest against the whitest background. And red will look most vivid against the yellowest background; and the same is the case with all colours when surrounded by their strongest contrasts. On the reflection of colours (281-283). 281. PERSPECTIVE.