enviornmental polution is major cause of making white to pale white or off white, weekly shampoo wash and wax protected paint resisit to said problems
i have seen many people wash car with simple water without car shampoo and than wax it, shampoo help to remove light oxidation / embeded dust, and simple water fail to remove these things and we apply wax on dirty skin means we seal in all oxidation
use stronger shampoo as white colour needs it , turtle heavy duty shampoo seems good choice than give polishing, ( scratch out is also a kind of polish to remove minor imperfections, remove oxidation etc ) than seal it with good sealant or wax.
many body shops in city doing this things but what i observe they dont use quality products , dc studio under construction and going to open by end of next month or max early march , qualified personnel will be there with worlds best detailing stuff at reasonable price.
wax shop will be also there at very competitive rates
u should use synthetic waxes like megs nxt or 3m performance finish , mother synfx , turtle ice polish , nxt is most expencive and turtle least
synthetic waxes provides best protection for longer time 
