With an electrochemical treatment, it is possible to increase the thickness of the naturally protective oxide film present on the surface of valve metals such as tantalum, titanium and its alloys. Oxide film thickness can then range from 10 nm to more than 250 nm. Interferences phenomenon explain the bright colors obtained. Besides decoration, the coloring can be used for marking. This can be of practical interest for the quick recognition of different medical devices in operating theaters. For this application, the reproducibility and uniformity of the color is crucial and our processes have been optimized for this purpose. We can also process a special coating on Ti and its alloys using a porous anodisation technique. The sample color is then metallic gray and its surface exhibits a stochastic arrangement of small pores (100-200 nm).