Watermark coefficient selection for color images, and the amount of inserted data in a human visual system have problems in robustness and invisibility among watermark requirements. As the technique that inserts watermarks uniformly in every image in different color spaces causes color alterations and image quality deterioration, watermarks should be selectively inserted in visually less sensitive places. In addition, watermark insertion is needed in devices with various features such as computers, PDAs and mobile phones as users want to use multimedia services on those devices. This paper suggests a watermark insertion technique for color images by selecting frequencies to insert watermarks in Y components that correspond to spatial locations, which are less sensitive to chrominance signals, and creating insertion keys that consider properties of frequency coefficients in multi-level structures. Therefore, insertion, invisibility and robustness of watermarks against JPEG compression for multimedia contents in devices with various performances can be quaranteed.