Barrymore Scherer has a fine essay on Charles Marion Russell, a peer of Frederic Remington, who worked in watercolors. That gives Scherer the opportunity to offer a brief disquisition on history of watercolor in American art:

This is not just a show of Russell’s watercolors but also about Russell’s often innovative watercolor technique. Russell’s affinity for his preferred medium coincided with a general surge in watercolor activity following the Civil War, when commercially manufactured paints and papers became increasingly available for mail-order shipment. Earlier, John James Audubon had made his meticulous ornithological studies in watercolor, and artists like Thomas Sully, Asher Durand and George Caleb Bingham painted and sketched in watercolor. Nevertheless, the medium had been a lesser ancillary to oil painting until Winslow Homer emerged about 1875 as the first important American to embrace both transparent and opaque watercolor for their own unique properties, rather than merely to add color to line drawing.

Although Russell’s work doesn’t exhibit Homer’s bright Impressionist palette or his sometimes innovative sense of compositional space, he often uses looser brushwork for backgrounds and foregrounds of his compositions, while painting his figures tightly—a manner allied to the French juste milieu style that influenced Paris-trained contemporaries like Sargent and Daniel Ridgway Knight.

At Home on the Range (Wall Street Journal)