Paper that Changes Colour

I checked some material out of the library today and it asked if I'd like a receipt with due-date.

I thought - how about something that gets exponentially redder as the due-date approaches - maybe options you can set on the screen - no change until within 5 days, etc.

Then, at T-4, it's light pink, at T-1, it's really-really red.

How do we accomplish this and keep it cheap? Then you could just put the receipt on your fridge and not miss it since most fridges are white.