Notice the difference between these two “paintings?” The one above is a virtual re-creation using some amazing science techniques. You can read the article here. It’s really interesting. Evidently Van Gogh was using a paint color that was not long lived. In the painting below, that particular color has faded. In doing the scientific examination, they were able to add that fleeting color back in, as seen in the virtual painting above. The source for the painting below is here.