Not to flame you but it could be like yo said with the lighting and all but thats what my flowmaster tips look like when they are dirty +1
on the windex and steel wool works wonders.

 

i ****in hate dirty tips[:@] i clean all my carbon build up that gets in my slp tips with paint thinner. works like a charm. been using it for a year. gets it shining like new everytime.

 

think like sand paper, the 000 steel wool is finer and whill do less damage to the finish

 

i tried windex today just wasnt doing it

i use a steel woll i dont know why i said sos pad

the aluminum polish was getting it shining better

the driver said tips have a permanent black streak to them i cant get it off. i was scrubbing for a good 20 mins wasnt doing anything so i gave up.

and believe me it was the light cus i took the car to my buddyes and parked in the sun and first thing he asked me was if i got new tips haha

 

for that black stuff, try like a paint thinner or mineral spirits. I'm telling you try some of that neverdull stuff (see if any of ur friends have some), it shines mine up like a mirror...