This letter presents an efficient video coding algorithm in the RGB color space. Currently, most video coding algorithms are based on a decorrelated color space such as YUV or YCbCr, which has reduced inter-color redundancy. For high-fidelity video applications, however, it is essential to maintain the original signal fidelity without any mismatch in color space conversion. In this context, the H.264/AVC High 4:4:4 Intra/Predictive profiles support the RGB color space to satisfy increasing demand for high-fidelity video coding. However, very little effort has been made to utilize inter-color correlation to increase RGB coding efficiency. In pursuit of both high-fidelity and coding efficiency, we propose an adaptive inter-plane-weighted prediction algorithm exploiting inter-color redundancy of the RGB signal. We integrate the proposed algorithm into H.264/AVC High 4:4:4 Intra/Predictive profile reference software for simulation, and show that the proposed algorithm increases RGB video coding efficiency at average 0.80 dB and 0.75 dB, compared with the existing H.264/AVC High 4:4:4 Intra profile RGB and YCbCr 4:4:4 coding, respectively.