In this article, we study the color appearance of the ink printed on a background, according to both its concentration and the background color. We find some attributes, the concentration quotients ratios, that are more invariant to the ink concentration than simple color attributes. Our work deals with traceability of porcine products. We have to detect the animal identifier, printed with ink on the pork rind. Using the concentration quotients ratios, our segmentation technique succeeds for any quantity of ink and any hue of pork rind. This technique could be applied to segment any set of pixels, that are colorimetrically and spatially close, but nor necessarly all connected.