This is a test of commonsense. Complete the next sentence:

How to remove hair dye from a wall
Test the alcohol on a small area.
Wet a cotton ball with alcohol and rub it on an inconspicuous spot on the wall, first. Check for stains, discoloration, or residue.
If the alcohol produces any unwanted affects, then try a different method. You should always test products and solutions on small, hidden areas first before using them on larger surfaces to avoid unwanted effects.