In this paper, we propose a method to embed the color information of an image in its corresponding grey-level image. The objective of this work is to allow free access to the grey-level image and give color image access to secret key owners. This method is made of two steps which are the color image decomposition (in a grey-level image and its associated color information) and the data-hiding. The main contribution of this paper is the energetic function proposed to model the decomposition of the color image. The optimization of the proposed energetic function leads to the obtention of an index image and a color palette. The good properties of that decomposition are an index image which is similar to the luminance of the color image and a color palette which is well suit for the data-hiding. The obtained results confirm the model quality.