How can ‘colour’ be considered a distinct element of Louis Ouinze Art?

Directions: Read the following passage and answer the question.
Fanciful as the Louis Quinze art seems, by contrast with that of Louis Quatorze, it, too, is essentially classical. Watteau, Fragonard, are as gay, as spontaneous, as careless, as vivacious as Boldini. Their very names suggest not merely freedom but a sportive and abandoned license. But in what a narrow round they move! How their imaginativeness is limited by their artificiality! What a talent, what a genius they have for artificiality. It is the era par excellence of dilettantism, and nothing is less romantic than dilettantism. All their material is traditional. Of ideas they have almost none. They are as barren of invention in any large sense as if they were imitators instead of, in a sense, the originators of a new phase.
Yet they have that distinct quality of charm which is eternally incompatible with routine. They are as little constructive as the age itself. Of everything thus indicated one predicates at once unconsciousness, the momentum of antecedent thought modified by the ease born of habit; the carelessness due to having one's thinking done for one. But out of this very condition of things, and out of this attitude of mind, arises a new art, or rather a new phase of art, essentially classic, as I said, but nevertheless imbued with a character of its own, and this character is distinctly charming. Wherein does the charm lie? In two qualities, I think, one of which has not hitherto appeared in French painting, and that is cleverness in the use of color. The Louis Quinze painters were sensitive to that vibration of atmosphere that blends local hues into the ensemble that produces tone. The ensemble of their tints is what we mean by color. Since the Venetians this note had not appeared.
By cleverness, as exhibited by the Louis Quinze painters, I do not mean mere technical ability, but something more inclusive, something relating quite as much to attitude of mind as to dexterity of treatment. There is a sense of confidence and capability in the way they view, as well as in the way they handle the light material. To be adequate to the requirements - rarely very exacting in any case - never to show stupidity, to have a great deal of taste and an instinctive feeling for what is elegant and refined, to abhor pedantry and take gayety at once lightly and seriously, and beyond this to take no thought, is to be clever; and in this sense the Louis Quinze painters are the first, as they certainly are the typical, clever artists.