Letter from Vincent van Gogh to Theo van Gogh, Saint-Rémy, 11 or 12 May 1890 [letter 633]: "I am doing... 2 canvases representing big bunches of violet irises, one lot against a pink background in which the effect is soft and harmonious because of the combination of greens, pinks, violets. On the other hand, the other violet bunch (ranging from carmine to pure Prussian blue) stands out against a startling citron background, with other yellow tones in the vase and the stand on which it rests, so it is an effect of tremendously disparate complementaries, which strengthen each other by their juxtaposition. (http://www.tfsimon.com/auvers-sur-oise.html) In May 1890, just before he checked himself out of the asylum at Saint-Rémy, Van Gogh painted 4 exuberant bouquets of spring flowers, the only still lifes of any ambition he had undertaken during his yearlong stay: 2 of irises, 2 of roses, in contrasting color schemes and formats.... (http://www.metmuseum.org/art/collection/search/436528)