Flatten PDF Drop-down list transparent background

[Lau5CC9]

Is there a way to flatten a PDF form and for the drop-down liste to stay transparent?

The other field are ok but the drop-down list change to a white background.

[Karl Heinz Kremer]

I am not aware of anything you can do to change that. You either get the field background color if the field background is set, or the field highlight color - at least that's what my experiments showed. 

[try67]

I just tried flattening a transparent drop-down field and it stayed transparent even after being flattened, and even the arrow was gone. Just the selected text remained.

Are you sure the fill color was set to No Color? Also, how did you flatten it, exactly?