Automatic E-mail

Question

Hi I am looking for a code that when a cell changes YELLOW, I want an email to send automatically to that person and when the cell changes RED another e-mail to be sent to them.

The cells contain expiry dates of mandatory training and are:
- GREEN when in date,
- YELLOW when they have 29 days before they are out of date AND
- RED when they are a day over the date that their training expires.

The e-mails are to prompt them to book onto a course when they are YELLOW (almost out of date) and to input there new expiry date when they get an email when it turns RED.

Hope that all makes sense.

Formula for it to turn green: GREATER THAN =NOW()+30
Yellow: BETWEEN =NOW() =NOW()+29
Red: LESS THAN =NOW()-1

Can these codes work in the background when the spreadsheet is closed or does it only work when the spreadsheet is open? Also can the code be used without Kutools.

Thank you in advance, Alyssa