Help needed - removing exhaust soot from bodywork

[Freakuk]

We've all seen it back end of a car and the bodywork/bumper area around the exhaust looks tired with exhaust soot etc engrained around the area.

I'm starting to seen the same, the cars less than a year old but white, because it's white it gets cleaned pretty much every weekend but around the exhaust tips it's looking decidedly grey.

Spent some time yesterday applying so road and tar remover with fairly good results, it's now a lesser shade of grey but still not 100%, the question is what can I use with good results to bring back the white?

Any ideas much appreciated.

Thanks

[Refined Detail]

Clay bar followed by polishing is usually the key. If it's cleaned regularly and there's a decent sealant / wax on the paintwork it shouldn't be too much of an issue to keep at bay. It's usually on cars that have been left a while that it causes further discolouration that can only be rectified via machine polishing