Final answer:
The Impressionists used optical color to allow the eye to mix colors for a more vibrant effect, employing techniques like side-by-side pure color placement and the use of complementary colors to intensify brightness.
Step-by-step explanation:
The Impressionists were interested in optical color, where it is the human eye that mixes the colors when viewing the painting from a distance. Their distinctive technique involved painting small strokes or dots of pure color side by side rather than pre-mixing the colors on a palette. This approach allows the colors to blend in the viewer's eye, creating more vibrant colors and luminous effects. Moreover, the use of a light-colored background and the strategic placement of complementary colors next to each other were crucial to enhance the intensity and brightness of the paintings.