I have two wood stoves. One is on the third floor and uses simpson duravtech double wall insulated stainless chimney. This chimney vents at the peak of the roof and is well above any part of the roof. This chimney has been in place for three years. The other stove is on the first floor and uses Selkirk Supervent insulated stainless chimney inside a chase running through the second floor and enclosed knee wall space of the third floor. It penetrates the roof about 3 feet in from the eve. Both chimneys draw fine. The chimney servicing the first floor is only two months old. I am concerned about some discoloration on the outside of the chimney about 1 foot below the cap. A slightly bluish tint, like over heated metal. I have a thermometer on the single wall portion of the stack just above the stove which is always running between 250 or 350 with an occasional to rise 400/500. I have access to the chase and the insulated chimney sections are never uncomfortable to touch. Could it be that the discoloration is coming from the exhaust gasses draping down the outside of the chimney? The third floor chimney shows none of this discoloration.