Monet painted on canvas which was a light color, such as white, very pale gray or very light yellow, and used opaque colors. A close-up study of one of Monet's paintings will show that colors were often used straight from the tube or mixed on the canvas. But that he also scumbled colors -- using thin, broken layers of paint that allows the lower layers of color to shine through.
Monet build up texture through his brushstrokes, which vary from thick to thin, with tiny dabs of light, adding contours for definition and color harmonies, working from dark to light.
