Hi,
The issue occurs when there is a secondary aerial on TIN. A shader try to get color details from the TIN and apply it on the custom aerial.
We have found a fix but it will probably not be ready for SU2.
However there is a workaround, a polygon with “exclude TIN” will allow to only display the secondary aerials. But it will cause discontinuity on the border of the polygon (you can see that on your second screenshot, there is a exclude TIN on the left side causing these white blocks).
So be sure to make it larger than the second aerial zone.
Regards,
Xavier / Asobo