Changing Cell colour on input of certain word

I have received a spreadsheet in regards to my job and have been advised that when I enter the words "to", "from" or "and" in the same column, the cell changes to a specific colour depending on the word I enter. Unfortunately I have lost contact with the author of the spreadsheet and was wondering if anyone knew how this is done?

If you can help please contact me as I am intrigued to find out how it has been done.

Many thanks.