The Nostalgia shader does exactly the same only with a different palette.
I've updated Nostalgia so the user can select presets and the EGA palette will produce the same result if you first multiply the input color by 1.2 (this can be done with Lift Gamma Gain - it's a gain setting)
a round to 2-bit per component will yield 6 bit color so 64 color.
This reduces it to 16 colors.
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