2 of 4 pipes bluing??

[McyMike]

On my Yosh TRS system my two right outside header pipes have turned blue. The other two (left) are fine. I 'm guessing I'm running lean on those two cylinders (but how?) can anyone explain?

PS: Running NOS, but it sprays in the center of the air box, not the right or left tube. Fuel mixture stays rich while spraying according to dyno sensor.

 

[Johnnycheese]

which stacks and which airbox?

 

[McyMike]

Johhny any ideas? No stacks. Fully modded air box with K&N. Pair is gone. On the dyno I showed
plenty rich across the board. I don't spray the NOS much (duration is only 2-3 seconds at a time) so I don't think the heat came from that.