Abstract: Described herein is the use of a combination of organic additives that is particularly advantageous for the preparation of cementitious compositions having a high conservation of the degree of white, which contain in mass a photocatalyst that is able to oxidize, in the presence of light, air and ambient humidity, pollutant substances present in the environment, the said photocatalyst being, in particular, titanium dioxide prevalently in the form of anatase. The above combination of additives comprises the following: a melamine resin; a cellulose ether; a polymer chosen from among an ethylene polymer, an acrylic polymer, and a terpolymer comprising as co-monomers at least one ester of acrylic acid with an alcohol and at least one ester of vinyl alcohol with a carboxylic acid, or alternatively, an acrylic, styrene or butadiene latex; and a chemically modified starch.