I ran it down, because I was curious. Title 47, 12-218 defines what lights an unmarked car must use if it is for traffic enforcement. No mention of uniforms.
So, yes, you must stop, and no, they may not be in uniform except most agencies seem to have that as a policy. I am happy to be wrong if this is defined elsewhere in the state code.
B. A law enforcement vehicle when used as an authorized emergency vehicle may but need not be equipped with alternately-flashing red or blue lights specified herein. An unmarked vehicle used as a law enforcement vehicle for routine traffic enforcement shall be equipped with the following combination of lights:
1. Three flashing red, blue, or a combination of red and blue lights emitting the flashing lights to the front of the vehicle;
2. Two flashing white lights emitting the flashing white lights to the front of the vehicle;
3. Flashing red, blue, white or any combination of red, blue or white lights placed at and emitting the flashing lights from the four corners of the vehicle so that they are visible for three hundred sixty (360) degrees; and
4. One flashing red, blue, amber, or any combination of red, blue, or amber lights emitting the flashing light to the rear of the vehicle.
C. The use of the signal equipment described herein shall impose upon drivers of other vehicles the obligation to yield right-of-way and stop for authorized emergency vehicles, as prescribed in Section 11-405 of this title.
So, yes, you must stop, and no, they may not be in uniform except most agencies seem to have that as a policy. I am happy to be wrong if this is defined elsewhere in the state code.