If a booking is yellow on your grid, it means there is a notification relating to that booking e.g. an email to failed delivered or a new booking was created.
Clicking 'Show on grid' will show you which booking the notification relates to on the grid. This is helpful if you have a lot of rooms and not to sure which booking is affected.
If you click 'Next' on the notification, it will remove the alert and the booking colour will change back to normal .