I've had this problem for a few years now and it really bugs me. Thepassenger side tail lights are dimmer than the drivers side ones, whether I hit the brakes or the lights are on, they are always dimmer. My passenger side headlight is also dimmer than my drivers side head light, not a lot just barely noticable, so I don't think the ground has come out of the assembly, also all the light flicker just a little bit while my car idles (800 RPM). Also my back up lights are so poop they're now just for legal purposes only. None of the lights are brown , just dim, and only on the passenger side of the car. 1986 TA LG4

 

got to be a ground problem check and clean them all, might have the green groweys on them. If you have a VOM you might check each side and see if the ohms differ from side to side

 

Headlights: One could have been replaced. Try swapping them left-right and see if the same bulb is dim.
Taillights: Make sure they are all the same number. a 2057 is brighter than a 1157--but both fit the same size socket and will work. Flicker at idle is usually the alternator not keeping up and/or the internal voltage regulator is toast.