It looks like the API is doing some conversion and ignoring transparency. When viewing the image directly, this is the result:
Description Image:
https://cdn-wow.mmoui.com/preview/pvw75701_thumb.png
Screenshot Browser:
https://cdn-wow.mmoui.com/preview/pvw75701.png
Actual Image: (Older version, but still transparent)
https://wago-addons.ams3.digitalocea...k2HWBlrQPC.png