Mechanically, I have got the new carbs. I had to re-shape the middle 1/3rd of the primaries on 1,2,3. The top/bottom 1/3rd of the primaries is still the original stainless and has colored normally (like 4,5,6), it's only these middle 'new' stainless bits that are going a very different blue color. I also made sure to keep them equal length.
I thought like you that is was heat, but then the top should be as hot or hotter than the middle of the primary. Strange huh?