Theoretically, only RGB-implemented colors which might be really spectral are its primaries: red, green, and blue, whereas any other (mixed) color is inherently non-spectral. But due to different chromaticity properties of different spectral segments, and also due to practical limitations of light sources, the actual distance between RGB pure color wheel colors and spectral colors shows a complicated dependence on the hue. Due to location of R and G primaries near the almost "flat" spectral segment, RGB color space is reasonably good with approximating spectral orange, yellow, and bright (yellowish) green, but is especially poor in reaching a visual appearance of spectral colors between green and blue, as well as extreme spectral colors. The sRGB standard has an additional problem with its "red" primary which is shifted to orange due to a trade-off between purity of red and its reasonable luminance, so that the red spectral became unreachable. Some samples in the table below provide only rough approximations of spectral and near-spectral colors.