Why my complication icon on watchos7 showing a white block

my program implemented a complication that will show on watch face. Before I update to watchos7. the icon of complication showing well on watch face. but after I upgrade to watchos7, it show as a white block. who have any idea how to debug it?


BTW, some information amend.
I found the requirment of complication image on ["Designing Expressive Complication Content
"](https://developer.apple.com/design/human-interface-guidelines/watchos/overview/complications/)

Provide complication images in PNG format. Avoid using interlaced PNGs. Complication images use only the alpha channel of the image.

What is that mean? does it mean the complication icon only use the alpha channel of the image, so it just support single color?
if I want to use color icon in here, can I do it? and how?
Why my complication icon on watchos7 showing a white block
 
 
Q