Calendar multi view: show booking in a different colour if not paid

I would love to be able to see easily on the multi calendar view if there are upcoming bookings that have not been paid. Change the colour to red, for example, instead of green. This applies especially for direct bookings over the phone, after I sent them a link to the guest portal to pay. It can be difficult to remember to keep track of who has paid, and too late to start chasing them on the check in date (which can then lead to guest not arriving, resulting to lost revenue). Thank you!