Sadly that is in fact totally wrong. There is more than sufficient colours inside an 8bit colour space.
The color gamut does not have to do with what colors fill up the 8 bit color space, that's the color depth. Color gamut concerns what that color space is -- what physical wavelengths the R, G, and B primaries have. The current standard for video, rec. 709, has R/G/B primaries and hence the color space defined in a way that the resulting color space is substantially smaller than that of human vision. The new standard, followed for UHD blu-ray, rec. 2020, has a wider gamut, but still smaller than the range of colors we can see in nature.
Here is an excellent online reference on color gamut. It will help you get oriented.
The Pointer's Gamut 
