Clean a small section of the wall to remove dirt and dust
Find the paint brand, color name, and finish from leftover cans or records
Take a removable sample from an inconspicuous area if needed
Bring the sample to a paint store for color matching
Use a color-matching app or handheld color scanner if available
Compare the match under the same lighting as the wall
Test the matched paint on a small hidden spot
Let the test patch dry completely before comparing
Adjust for sheen, since flat, eggshell, satin, and gloss can look different
Mix the paint thoroughly before applying to the wall
Paint a larger test area if the first match is slightly off
Recheck the match at different times of day before final painting