Stock out indication considering safety stock

Hi,

I am trying to find an indicator warning my vendor schedulers that we will have a stock out within a certain period. The problem is, that the exception message gives me a "red traffic light" when the safety stock is used. Up to now we did not find a way how to identify a total stock out. We would like to have the following indications:

green: stock is above safety stock in defined period

yellow: stock falls below safety stock but not below 0 in defined period

red: stock falls to 0 or below in defined period

Has anyone an idea how we could set up a error message / indication as described above?