Got a 4. Not perfect but hopefully good enough, since colour correction is part of my job description.
Seing hues correctly is one thing, but there is so much more to colour perception. Room lighting for one, which is why my poor colleague sits in a dark dungeon with a neutral, 50% grey backlit wall that drives you nuts after an hour. Looking at certain colours too long and those receptors get exhausted. Even your physical condition plays a huge part. If you're tired, have a cold or just had a cup of coffee - since that influences how much blood flows through your retina.
Sometimes we keep looking at an image over a period of weeks and tweak it ever so slightly to and fro until it looks right.
We should have never evolved beyond monochrome!