Hi Josh,
One (advanced) approach to monitor the timeline of "Feeder" projects (e.g. Project A) is to create a special section of your workplan (e.g. at the top of Project B, under a "Feeder Projects" parent task, for easy collapse/show convenience) with one task for each such dependency (e.g. "Project A Task XYZ"), with a cross project predecessor (e.g. finish to finish) back to that actual task in the feeder project, but (here's the trick) with no other dependencies or predecessors upon it.
In Project B, you can then set the planned completion date (e.g. to the latest date possible after which -- if Plan A Task XYZ "missed" -- you would then need to then revise the plan; presumably the same as Plan A Task XYZ's real Planned Completion Date, or later, if you have some slack available).
The beauty of this approach is that you can then "see" such Feeder project tasks within Plan B and (thanks to the cross project predecessor) more easily monitor their projected dates as the Feeder Project changes, either on the Gantt view (where a delay on Plan A will then appear, if you turn on Projected Dates, as a "slippage", visually), or (returning to your original question) by highlighting the color of a cell in red whenever the projected completion date is later than the planned completion date.
You can repeat this approach for each Feeder project/task of interest as needed, and for complex systems, even "chain" multiple feeder projects together, which is then where our Timeline solution comes in: it lets you choose one or more Critical Tasks, set their Path Colors, then view Timeline to trace the resulting multiple Critical Paths through all predecessors and feeder projects.
Thanks for raising the question: I'm interested to hear how you make out!
Regards,
Doug