Defective Paint Advice

[bmw_convert]

Hi..My X6 Space Grey has undergone a respray / coat at the dealership several months ago. I am happy with the work done but I have noticed that at night and under certain light conditions such as under yellow street lamps, at the gas station, basement parking at the office etc..there's a two tone patch (approx 20 inches wide) at the rear end around the gas tank. The patch clearly has a very lighter tone compared to other areas. Something like liquid wax that have not been thoroughly wiped off but is under the clear coat.

Under sunlight and normal conditions, its totally unnoticable. However, I am finally due to sent the car back to the dealer for some other minor defects (overspray). I would appreciate to have some feedback / advice from members knowledgeable about paints here. Sorry unable to take a pic as I think its more visible to the naked eye and under certain light only. Any advice is much appreciated. Thanks!