I dont think FBI, DEA and BATF agents make routine traffic stops?
Here in Texas a local PD uses red and blue with a yellow light in the middle, the yellow in the middle may be optional?
The drivers manual for the state of Texas says flashing red lights....
If the driver is unsure of an unmarked unit thay should probably call 911 and give thier location to the dispatch and they will probably get an answer shortly.
Have a nice day at the range
NRA Life Member