That vivid colour demands the comparative absence of colour, either on a lighter or darker scale, as its contrast, may be inferred again from the fact that bright colourless objects produce strongly coloured spectra. In darkness, the spectrum which is first white, or nearly white, is followed by red: in light, the spectrum which is first black, is followed by green (39-44). All colour, as the author observes (259), is to be considered as half-light, inasmuch as it is in every case lighter than black and darker than white. Hence no contrast of colour with colour, or even of colour with black or white, can be so great (as regards lightness or darkness) as the contrast of black and white, or light and dark abstractedly. This distinction between the differences of degree and the differences of kind is important, since a just application of contrast in colour may be counteracted by an undue difference in lightness or darkness. The mere contrast of colour is happily employed in some of Guido's lighter pictures, but if intense darks had been opposed to his delicate carnations, their comparative whiteness would have been unpleasantly apparent. On the other hand, the flesh-colour in Giorgione, Sebastian del Piombo (his best imitator), and Titian, was sometimes so extremely glowing[1] that the deepest colours, and black, were indispensable accompaniments. The manner of Titian as distinguished from his imitation of Giorgione, is golden rather than fiery, and his biographers are quite correct in saying that he was fond of opposing red (lake) and blue to his flesh[2]. The correspondence of these contrasts with the physiological phenomena will be immediately apparent, while the occasional practice of Rubens in opposing bright red to a still cooler flesh-colour, will be seen to be equally consistent. The effect of white drapery (the comparative absence of colour) in enhancing the glow of Titian's flesh-colour, has been frequently pointed out:[3] the shadows of white thus opposed to flesh, often present, again, the physiological contrast, however delicately, according to the hue of the carnation. The lights, on the other hand, are not, and probably never were, quite white, but from the first, partook of the quality of depth, a quality assumed by the colourists to pervade every part of a picture more or less.[4] It was before observed that the description of colours in words may often convey ideas of too positive a nature, and it may be remarked generally that the colours employed by the great masters are, in their ultimate effect, more or less subdued or broken. The physiological contrasts are, however, still applicable in the most comparatively neutral scale.