This stamp commemorates the death of Mendeleev (February 1907), one of the lead figures responsible for the periodic table. Absolutely excellent choice of colours if I might say so! The stamp was sent to me by Prof Gabriel Pinto (Departamento de Ingeniería Química Industrial, ETSI Industriales, UPM, Madrid, Spain) and I quote from his web page:

"This stamp was launched on february 2, 2007, by Correos (Spanish Post Office). It is devoted to Chemistry with the periodic table of elements of Mendeleyéiev. It refers to the periodic classification of the chemistry elements proposed by Dmitri Ivanovich Mendeleyéiev in 1869. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his Periodic Table which described elements according to both weight and valence and which, if arranged according to their atomic mass, exhibited an apparent periodicity of properties. Unlike other contributors to the table he predicted the properties of elements yet to be discovered and made an accurate prediction of the qualities of germanium, gallium, and scandium which came to fill in the empty boxes of his table. Mendeleyéiev (1834-1907) made other important contributions to chemistry such as studies on the expansion of liquids with heat, the invention of pyrocollodion, a kind of smokeless powder based on nitrocellulose and made important contributions to the determination of the nature of such indefinite compounds as solutions. He was the author of Principles of Chemistry, a classic on the subject and for a couple of years was responsible for the Department of Weights and Measures of Saint Petersburg."