I'm not sure you understand, there are no 'real' RGB values. The NES outputs an encoded composite signal that has to be translated back into RGB by the display. The chips simply don't have RGB numbers for the colours. And how a display translates the composite varies wildly, which is why there are so many palettes available. Most TV's tended to boost the colours, and emulators often 'eyeballed' their palettes, making them too bright and garish. However, 'accurate' palettes can look too dark and dull due to most displays boosting the colours.
There is no 'real' palette, however you could try;
1) FBX Composite Direct - The most 'accurate' translation of the composite signal.
2) NES Classic - An 'official' one by Nintendo.
3) Wavebeam - My favourite, not too dark like FBX's but not too garish like emulators.
Hope this helps