In order to improve the storage efficiency of the quantum color image, a new method of describing quantum color image is proposed.In the proposed method, the positions of the pixels are described by the basis states of a multi-qubits system, while the grey value of three primary colors of the pixels are described by the phase of only one qubit.By using this method, several simple operations of the quantum color image are firstly presented, including the change and swap of grey values of three primary colors, and the flip and swap of the positions of the pixels.Then a new method of implementing quantum image watermarking is introduced.The proposed method can run on quantum computers in the future. The simulation results on the classic computer show the effectiveness of the proposed method.