This paper presents a new watermarking technique in spatial domain expressly devised for color images, which is based on transmit diversity techniques. The RGB tones of color images are considered as three independent slowly fading channels. Modulated by different pseudo- random sequences and interleavers, the same watermark in different forms is put into three color channels simultaneously. This scenario makes up the weakness in single color channel schemes that a single color channel is prone to severe fading. HVS characteristics of three color channels are separately considered. We use two extraction methods: one is comparing energy strength of three channels, the other is accumulating the energy of three channels. Experimental results demonstrate the unmistakable advantage of our new approach over algorithms operating on single color channels. Contrasted by the present spatial watermarking schemes, this algorithm is considerably robust to many intentional and unintentional attacks.