An old trick in detective shows and movies was that a person could rub a pencil over the top of a notepad of paper, and sometimes the message (on the sheet that had been torn off above) could be read because the original writer had pressed so hard.

But people don’t use notepads as often now. Lots of places use those whiteboards with various colored markers.

Is there residual color memory? Could a forensics person piece together what was written on a whiteboard even if it had been erased, based on some invisible chemical remnants?