A new blind watermark algorithm for color image was proposed. First, the green component of the original image was blocked by size 8×8 pixels and transformed with discrete cosine transformation (DCT). Second, two chaotic sequences were generated by logistic mapping, and the binary watermark image was scrambled by the chaotic sequences and spread spectrum modulated by two uncorrelated random sequences. Third, the modulated watermark was embedded in mid-frequency region coefficients of DCT domain. At last, the watermarked image was obtained by inverse discrete cosine transform. The watermark was extracted by comparing the correlation between two random sequences with watermarked image, the process did not need the original image, namely a blind watermark algorithm. Experimental results demonstrated that this method is invisible and robust against some usual attacks such as JPEG compression, cropping, adding noise, and embedding watermark in green component is more robust against lossy compression than embedding watermark in red or blue component.