The present invention deals with a composition for evidencing bacterial plaque based on natural colorants comprising at least one concentrated solution of natural colorant selected from the group consisting of colorants extracted from the aai (Euterpe oleracea) and colorants extracted from urucum (Bixa orellana), in a pharmaceutically acceptable vehicle and, optionally, acceptable pharmaceutical additives. Preferentially, in the case of the aai solution, the concentration varies from 60 to 95% of concentrated extract, whilst for the urucum solution, the concentration varies between 56 and 90% of concentrated extract.Also preferentially, in solutions containing a mixture of the extracts, these will be present in a proportion that varies from 10:1 to 1:1.