a report on this subject.
The researchers say that the current colors may not be the original ones. Interestingly, the ancient drawings are not being eaten by bacteria and fungi, instead they follow the lines meticulously. The researches suppose this is because the surface of the rock was etched, so that the micro organisms could grow. It may be that the original paint already contained the organisms.
Thanks to the light of the sun, the paintings have been kept 'alive' for thousands of years. It appears that the micro-organisms are very well able to adapt to changes in humidity and temperature. This may be the secret of the longevity of the drawings.