How to make a cell color change automatically depending on the user entering data into this cell?

Question

Google Sheets

There is a table which is allowed to be edited only by three users. It is necessary to make the cells edited by user 1 change color to blue, and user 2 to red, etc.

Answer 1

Use these things:
onEdit(event) to determine if the table has changed
Session.getActiveUser().getEmail() - to determine the current user's email
event.source.getActiveRange() - to determine the current cell
setBackground() - to set the desired color

function onEdit(event){
  if (Session.getActiveUser().getEmail()=="[email protected]") event.source.getActiveRange().setBackground("#FF0000");
};