Monet, Manet, Cezanne and Renoir were some of the more famous French Impressionist Painters. Others included Degas, Pissarro and Sisley Impressionism got it's name from one of Monet's Paintings: "Impression Sunrise" (Impression, Soleil levant). The French Impressionists were the first group of painters to paint from real life. They would take their paints out to the place they wished to paint so they could match the colours and light with their paints. This process was known as "En Plein-Air" painting (French for "In the Open Air). The artists painted very quickly as the colours would change as the light of the day changed.
Before en plain air painting, artists would sketch from real life but would take their sketches back into the studio to produce their paintings using the colours that they had learned to use at the European Art Academies These colours looked attractive and suited the style of painting but they were not necessarily the "real" colours of the landscape.
(Follow this link for a more comprehensive look at Impresionism).
The French impressionists found that under different lighting conditions colours changed. A dull day would use very different colours to a bright day. The strange light of a sunset caused some very peculiar colours.
The French Impressionist painters were more interested in painting the colour and light conditions of a landscape than to show the fine detail.
... Claude Monet - The Houses of Parliament at Sunset - 1903 ...
Claude Monet
"Water Lilies and the Japanese bridge" painted 1897-1899
Some of Manet's Paintings
Le Dejeuner sur L'Herbe
Boating
Berthe Morisat
Some of Renoir's Paintings
Le Pont Des Arts
La Grenouillere
The Seine at Asnieres The Skiff