To quote Dr. Goldratt's article "Standing on the Shoulders of Giants", as well as him mentioning this multiple times elsewhere in his videos:
... is an environment with high variability. The lesson that Shewhart brought to manufacturing from Physics, and Deming made known worldwide, is that trying to be more accurate than the noise (in our case, trying to use sophisticated algorithms that consider every possible parameter in an environment of high variability) does not improve things but makes them worse -- the results will most certainly not be an improvement but a deterioration in due-date performance.
Then he goes on to explain the concept of "buffer-management" that is quite simple and answers the question fully.
If less than one third of the time buffer has passed the priority color is green, if more than one-third but less than two-thirds the priority color is yellow, if more than two thirds the color is red, if the due date has passed the color is black. Blacks have higher priority than reds, etc.
And when Critical Chain Multi-projects are concerned, then this pearl of wisdom applies as well:
If two batches have the same color, to try and decide which one should be worked on first is an excellent example of trying to be more accurate than the noise.
Bottom line, take the full buffer length and separate into three. First is green, second yellow, third red. Any project that passed the red zone is considered black.
Priorities for management attention on what is important go the other way - black highest priority, then red, then yellow. Green is not a priority, as everything is going on as it should.