Human visual systems are insensitive to slight saturation changes in a color image. This paper presents a novel watermarking approach by hiding grayscale logos in the saturation component of color images. The embedding procedures are first performed in the DWT domains of the achromatic component. Then a proposed technique of saturation adjustment is applied to redirect the marks into the saturation component. To improve the detection robustness, we propose an adaptive weighting scheme to fuse the extracted watermarks in the extraction stage. Experimental results demonstrate that the proposed approach can successfully make the watermark perceptually invisible and robust to image-processing operations such as low-pass filtering, JPEG, scaling and cropping under StirMark, and JPEG-2000. Robustness can be provided in the applications of copy protection and digital archives.