Serra et al.’s study, entitled “Color combination criteria in Le Corbusier’s Purist architecture based on Salubra claviers from 1931“, has been published in 2015 in the International Journal “Color Research and Application“. This study has been realized by the Color Research Group at the Instituto de Iestauración del Patrimonio, and aims at studying the color combinations of the Salubra 1931 of Le Corbusier, by analyzing them in the Natural Color System, to understand the perceptive variables of colors (hue, blackness, and chromaticness) as well as their combination criteria.

This research aims mainly to study the color combinations selected by Le Corbusier in the claviers for the Salubra wallpaper company in 1931, by analyzing them in the color space of the NCS, in order to understand the perceptive variables of colors (hue, blackness, and chromaticness) as well as their combination criteria.
Furthermore, it aims to :

-studying the similarities and contrasts of the colors combinations and their perceptive variables
-analyzing the principles in Le Corbusier’s color preferences in his purist architecture
-provide a universal system related to some color combination rules pointed out by other authors regarding Le Corbusier’s colors.

The scholar Juan Serra has conducted a practical experiment in Le Corbusier Foundation in Paris, where
the original color charts were visually and technically evaluated (contact spectrophotometer Konica Minolta CM 700d, Munsell and NCS colorimeter). In the Foundation, many documents were analyzed as the writings, letters, technical specifications of the buildings, and other graphics and written material, in which the architect reflects on the use of color in his study.

As a concluding phase to this study, it has been concluded that :
1- The architect limits the palette to 43 colors and the white, which is assumed as a background in a minimum ratio between 33 and 50%, whereas the more vivid colors (with more chromaticness) should be limited to a ratio between 7.5 and 22%.
2- The colors have to help the understanding of the different pure volumes that make up a building and its hierarchy.
3- The architectural color is often explained by its associative connotations.
4- Plain colors are used and the color gradients are rejected.
5- The colors usually cover the entire surface of the architectonic element to be colored, except in some few cases.