In what ways is color blindness an issue in modern jet airliners?
There are lots of problems.


Sight is just generally important when flying. Even in airliners, most approaches are still flown manually and often visually. Any significant degradation of sight is going to be a problem when flying any type of airplane.
Red/Green/White light signals are used by air traffic control in the event of a radio failure. The inability to differentiate red from green in this case would be an enormous safety hazard (e.g. did tower just clear me to land or tell me to keep circling?)
PAPI/VASI lights use colors to indicate whether you're above, below, or on the proper glide slope for a runway. While it's possible to land without them, it's a significant reduction in safety.
Lights at airports are color-coded to indicate whether a particular road is a runway or taxiway, how close you are to the end of the runway, that a runway is in use, etc. Landing on a taxiway is usually a bad idea, so it's best if you can tell the difference.
The navigation lights on airplanes themselves are color-coded. The right wingtip has a green light, the left wingtip has a red light, and the back has a white light. This lets other pilots easily determine which way you're going and, in case of conflict, who should yield (seeing a red light on another aircraft means that they're to your right and, therefore, you should yield to [i.e. divert around] them.)
Colors are used on aviation charts to indicate all kinds of things, including class of airspace, type of special-use airspace, whether a field is controlled or not, type of route, elevation of terrain, where you should expect to see city lights at night, etc. You need to be able to distinguish these things quickly and accurately, even in low-light conditions.
Some cockpit instruments use colors to indicate various things. These include color bands on airspeed indicators, color of annunciator lights or their on-screen equivalents (i.e. red for warning, amber for caution, green for gear down, etc.,) echo intensity on a weather radar display, etc.