White pipe but normal plug?

[Strattos]

I've just been riding, and the bike's running perfectly, but when I stopped for a breather I noticed the inside of my end cap is white, which immediately got me worried about running extremely lean, despite the fact the bike appeared to be running fine.

I immediately put the bike on the ute and rushed home to pull the plug out. The plug appears fine. Any suggestions about why my pipe's white?

The riding isn't flat out, high speed, sustained top gear stuff or anything.

I normally plug my exhaust with a rag when the bike's in the back of the ute, and maybe the rag had some oil on it or something? But i've been using it for ages.

[642MX]

Are you using a leaded fuel?

The reason I ask is, leaded fuel leaves a white residue in the exhaust. Or at least on my bike it does.

[Strattos]

No. Unleaded. Seems bizzare to me.