Thought paint codes were in the option codes... But paint code on a 6 -17 year old truck is going to be inaccurate due to fading. You try to paint it to match where you are at today... Knowing that in the future they will fade differently and coloring different no mater what you do. Some colors show different shades (fade) better than others.
Most paint color providers have spectrometers that can identify the exact color your paint is today and you can match to that.
But again, that area will fade at a different rate then the area around it since it is starting out fresh as a slightly different color. And the fade rate could be different due to using different brand paints etc..