iOS custom Action extension uses a template image

[bob]

"In iOS, a custom Action extension uses a template image version of its containing app’s icon, which you must provide."—lack https://developer.apple.com/library/arc ... 14-CH5-SW1

This famously bad documentation is difficult to follow. Possibly it refers to some Photoshop feature or maybe even a Sketch feature. I use Pixelmator Pro. I have to make an icon for my custom Action extension (not a Share extension). By default what I get is a bizarro grayscale render of the app icon. Bizarro because its grayscale and looks like a photo negative.

What must I do in Pixelmator Pro and Xcode to provide an app icon with a template image that looks good?