Adeel bro, yes, i too second you on causes of bumper's shade difference.
About clay i am not convincing you on hardcore detailing and yes,i am saying about liquid clay not the clay bar,clay bar comes in hardcore detailing and is a step ahead.LC is easily available at good departmental stores as well as on montgomary particularly at saca.
its price is different in different cities of pakistan like in karachi saca are giving it for 650 pkr,from saca lhr you may get it for about 850 to 1050 pkr.
After shampooing the vehicle you will have to massage it with the applicator pad given in package,all little tar,bug and road grime stuck to the surface of paint which is hard to remove with shampoo only, can be erased with much ease and without damaging paint,surface will be quite dry after the use of LC but will be much clear and plain for the wax to work on.
its just like a pre make up cleanser which our women use at home.lolz