This is something that a lot of even very plugged into retrogaming people don't really get about the NES and RGB mods. I think it's very counterintuitive for people now that there is no part of the system that operates in actual 'color' information. The NES' video output is composite from start to finish[1], with palette entries corresponding to approximate output frequencies for the color subcarrier.
So there is no canonical palette for the NES - the colors produced by games varied by region, a little bit by unit, and especially because NTSC had trouble with stable color even by TV.
So people imagine that RGB or HDMI mods of the NES are somehow tapping into a missing layer of raw color information, but what it's actually doing is intercepting communications with the PPU and modelling (on an fpga) an extra PPU that does operate in RGB, and then constructing a new video signal from that.
And then you have to pick a palette, because there isn't just one.
I have an RGB modded NES (a US toploader) but I doubt I will ever buy or make another one. At this point I think it's better to just use an upscaler, which will produce no less authentic a picture. The main benefit imo of the rgb mod is that there's less interference so the picture is clearer, even if you just output reconstructed composite from it.
[1] There is actually a model of NES PPU that outputs RGB, it was used in the PlayChoice arcade machines (which generally used RGB monitors, not composite) and it has a palette that most people agree is ugly as sin.