The arrow is pointing to an echaust area for bleed air pre-cooling. The extracted bleed air is normally cooled to 200 degrees C (sometimes 150 degrees under certain conditions) prior to being routed inside the wing structure and that is where the excess temperature is vented overboard. I would imagine the colour change is due to the temperatures involved.

Dam , wys after his free vacations at TLS knows evrything about A34x 😉

Thanks for the info.