Abstract: Firstly a color constraint equation in the RGB color model was formulated in the paper based on the physical mechanism of color fusion for remote sensing image. Then the independent color constraint equation was proposed by introducing the YVC color model that must be suitable to color fusion of remote sensing images with different resolution. And the approximate solutions of the color constraint equations might be obtained by adopting the linear and quadratic equations. The computer simulation and the actual remote sensing experiment results showed that the color fusion effect could be significantly improved by using the approximate solution by applying the quadratic equations.