This paper introduces a new wide-gamut RGB primary set and a new color-encoding method that are developed for ultrahigh-definition television (UHDTV). The extended gamut RGB-primary set compared with the conventional CRT-centric gamut is proposed in favor of inclusion of real-world surface colors and in consideration of the current and prospective colorimetric characteristics of flat panel displays using which UHDTV programs will likely be reproduced. The new color encoding method is derived to enable luminance and chrominance information to be accurately separated, resulting in orthogonal video signals. The new luma and color-difference signals generated by the newly derived encoding scheme are demonstrated to have insignificant crosstalk. It is also shown that this fact can contribute to improving image quality after subsampling color-difference components and to increasing compression efficiency.