This paper deals with a method to protect the color information of images by providing free access to the corresponding gray level images. Only with a secret key and the gray level images, it is then possible to view the images in color. The approach is based on a color reordering algorithm after a quantization step. Based on a layer scanning algorithm, the color reordering generates gray level images and makes it possible to embed the color palette into the gray level images using a data hiding algorithm. This work was carried out in the framework of a project aimed at providing limited access to the private digital painting database of the Louvre Museum in Paris, France.