There is never one accurate palette, since every TV generates color differently with different color decoders. That said, Nestopia can accurately display any appropriate color TV decoder, given you have the R-Y, G-Y, and B-Y angles and gains. Nestopia starts out with a Consumer decoder, which is the one known as Sony CXA2095S/U. I've read that the default Canonical decoder is accurate for PAL games, but not NTSC games, and that a canonical decoder for NTSC TVs, which I've read is uncommon, would actually be shifted 15 degrees forward. If you test different encoders, you'll see that hues $2 and $8 are actually unreliable - $2 can be either a greenish or reddish blue, and $8 can either be a yellowish orange or a yellowish green. I'm not sure if this is inconsistent with Japanese NTSC-J TVs also; both of the 2 Japanese encoders that I know of make $2 a reddish blue and $8 a yellowish green.
If you're using a computer monitor (I believe LCDs especially), or any other monitor at brighter than default settings, you'll need to be wary of how you use certain color combinations. This can be a problem if you're mixing colors like $0c and $01 or $07 and $06; on a overly bright or high-gamma monitor, it may either look bad or even mess up the luminance order altogether. I made a thread about that
here. Set your computer monitor to default settings to see if it can roughly display the CRT gamma. I've read that LCD computer monitors (maybe not TV?) have linear gamma, so you may need to adjust your video card/palette to a gamma correction of 0.45 or so.
