If you have the original wall paint, you can have the paint store make you a quart with half the formula in it (you will need to provide the original formula and base). Many builders will paint the ceiling with a “half color.” We used Sherwin Williams white gold as our wall color. Our builder used 1/2 white gold for the ceilings (it makes the super white crown moldings pop).
In your small touch up roller pan, mix half of your original wall color with half of the 1/2 wall color. Try a small dab with a brush to see if it is a match. Keep adding from one or the other until you have found a match. Then use your roller touch up kit to touch up that faded wall!
With a sharpie, write a note on your paint can with the date and instructions on what you did to make a match so that you can replicate down the road. Let me know if these suggestions help you 🙂