On Purple and Yellow

More Ruskin (from Modern Painters Vol. I, Part II, Sec II, Ch. II):

I think the first approach to viciousness in any master is commonly indicated chiefly by a prevalence of purple, and an absence of yellow. I think nature mizes yellow with almost every one of her hues, never, or very rarely, using red without it, but frequently using yellow with scarcely any red; and I believe it will be in consequence found that her favourite opposition, that which generally characterizes and gives tone to her colour, is yellow and black, passing, as it retires, into white and blue. It is beyond dispute that the great fundamental opposition of Rubens is yellow and black; and that on this, concentrated in one part of the picture, and modified in various greys throughout, chiefly depend the tones of all his finest works. And in Titian, though there is a far greater tendency to purple than in Rubens, I believe no red is ever mixed with the pure blue, or glazed over it, which has not in it a modifying quantity of yellow. At all events I am nearly certain that whatever rich and pure purples are introduced locally, by the great colourists, nothing is so destructive of all fine colour as the slightest tendency to purple in general tone; and I am equally certain that Turner is distinguished from all the vicous coloursists of the present day, by the foundation of all his tones being black, yellow, and the intermediate greys, while the tendency of our common glare-seekers is invariably to cold, impossible pruples.