RGB color space has not been regarded as a proper space from a coding point of a view. However, due to the limited visual quality of YCbCr-domain video coding for high-quality applications, RGB-domain video coding is being newly raised. Recently, several methods have been developed to reduce significant redundancy existing between RGB color planes in an RGB video coder. This paper presents a new algorithm to remove inter-color redundancy, which is based on a linear model having two parameters, i.e., offset and slope information. Those parameters of one color component block are derived from the other color component block. A common coding mode and model parameters optimized for three color components in a macroblock are obtained simultaneously by minimizing a given cost. Then, a residue for each color component block is produced using its predictor based on the linear model, and is encoded. The simulation results show that the proposed algorithm noticeably improves the coding efficiency up to over 20% in comparison with H.264 new amendment.