The concept of pointillism is to create solid space of color by using dots of two or more colors in an area. French artist Georges-Pierre Seurat made this technique famous. His painting, Sunday Afternoon on the Island of La Grande Jatte (1884-1888) is one of the most famous paintings in the world. (Pictured below)
On the Art Institute of Chicago's website, it says "Seurat was only 26 when he first showed A Sunday on La Grande Jatte—1884 at the eighth annual and final Impressionist exhibition in 1886. In scale, technique, and composition it appeared as a scandalous eruption within Impressionism, a deliberate challenge to its first practitioners, such as Renoir and Monet. It immediately changed the course of vanguard painting, initiating a new direction that was baptized "Neoimpressionism." 
At left you see a closeup of Seurat's painting. It is a closeup of the the man laying down on the lower left. Even thought he appears to be wearing white pants, as you can see, the part of the pants in the shadow just above the grass has no white in it. It's only when you look at it from a distance that the colors blend in. Seurat spent two years on this painting. He carefully planned it out with several sketches first. You can find this painting at the Art Institute of Chicago.