Now Scott, I may be old and not up to the latest and greatest but outside of shooting in a studio with only studio lights with absolutely no ambient light, with a reference, you can achieve 100% accuracy.
Outside of that, I for one say it is impossible to gain 100% color accuracy outside of controlled conditions. In the studion you can shoot with a color key. You do need a key to match to get color accuracy. You shoot the key and then color correct the image so it matches the physical key you used. You apply these color corrections to the images you did shoot. For product shots, this is how it is done. For portraits, you typically do want to warm the subject some. In warming, you then go away from 100% color accuracy.
This is not to say you can't get close outside the studio. It simply takes a trained eye. You shoot and you color correct during processing to the eye of the person doing the processing like it has always been done. The reason why this is impossible outside of controlled studio conditions is because of ambient lighting. Sure you could use a reference such as gray card or color key card and process to match but that eliminates the color cast that the ambient light presents to the equation. After correcting, the end result would not be the reality of the scene.
Even with some of today's fabrics, it is impossible to get a color accurate image without affecting the color balance of the rest of the scene.
This doesn't even get into mixed lighting situations. You simply color correct the best you can when you process and hope to get close to the reality of the scene.
Again, what is your method to get 100% color accuracy of what you shoot?