How to extract binary/polygon mask for specific class using detectron2

[sparshgarg23]

So i am using detectron2 to run semantic segmentation on the below image.

This is the result.

From this result,I would like to extract the mask corresponding to the sky label and then set all pixels belonging to sky to the color white/255.

Is it possible,and if yes how should I go about it,
I was thinking of extracting the polygon corresponding to the sky label and setting all the pixels in that polygon to 255.
For this I feel that the issue #2245 may be useful.
Any ideas and suggestions would be useful