The approximate range of colors that the human eye can perceive is shown in the 1931 chromaticity chart (Kelly Chart) shown below:
The range of colors that can be generated, by a decent blue, an orange- red, and a yellow-green (not unlike the phosphors in color TVs) is contained within a fairly small triangle. If a decent yellow can be added at the right edge, then perhaps a green with less yellow can placed near the top left of the chart, greatly increasing the range of displayed colors contained within an odd shaped 4 sided figure. Getting past the limitations of the 3-gun CRT color (did anybody produce a 4-gun CRT?) may be a real plus for flat screen display.
jr