images from artrenewal.org
I have written about tonalism before. There is a search box up at the upper left if you want to find thgose. Sargent uses some tonalist ideas in a number of his paintings. Here are a few examples.
Above in the Jardin Du Luxemburg painting, Sargent has suffused the whole scene in a cool blue pearlescence. He is putting the picture into a unifying color theme. All of the colors except for a few red accents are variations on a color theme. This soft shade permeates the entire picture and is mixed into almost every note.
Lady Agnew above also has a tonal "drone" going on. That cool blue and soft blush pink is everywhere on the canvas. The trick to getting a tonalist effect is often as simple as suppressing its complement. That is if you want to paint a tonalist color based on yellow, you suppress it's opposite, violet. The color unity of the painting benefits enormously. This is the opposite idea of impressionist color in a way. The color is "corralled" into a narrow range, rather than observed in its actuality. Sometimes a plein air painting in accurate color can look like a mosaic of unrelated colors.
Here is another example, that glowing rose madder color is sneaking into just about everywhere in this painting. Sargent is "smuggling" red.