Digital watermarking is a technique for copyright protection. In literature, many watermarking methods for gray images have been presented. Some of them are directly applied to color images. However, how to choose one of the three components of a color space for watermark embedding is not yet studied. In this paper, we present an adaptive color image watermarking to solve this problem. The proposed method includes an improved wavelet-tree watermarking algorithm and two rules to elevate image quality and watermark robustness. Experimental results show the feasibility of the proposed method.