Feature Request Change Specific color to transparent

[ksy5662]

Dear wasabeef,

I have some feature request. I need to clean specific color and change it to transparent. Could it be possible to implement new feature or any suggestion that I can modify your class?

I want to remain only radar stuff and change background and seashore lines to transparent.. So

change this

to this

I just want to set cleaned image to the overlay of google maps

Many Thanks for your great work!!

[wasabeef]

@ksy5662

Your PR is always welcome.