I have a 2004 R6 with a D and D exhaust. I have noticed white dust around the end of the exhaust tip and it feels like the bike is running lean. Is there any reason that a slip on exhaust would mess with the mixture?
When aluminum "rusts" or corrodes, instead of showing up as reddish-brown, it shows as a white powder. I see a lot of this white powder develop on my engines that's not just road salt. Aside from that, some fuel additives can leave behind colored residue. One particular cleaner I used would color the oxygen sensor with a reddish hue. (like Mars)
As Broke suggested, check your plugs if you're concerned.