As the title says.
This happens even when not in dark mode.
Hi,
Here is feedback FB17549847. (Sorry for posting in Japanese)
Actually, after reviewing the data in the bug I think what you're seeing is actually the correct behavior. The purpose of the dark/light icon variants is not simply to provide the correct icons in dark/light mode, it's also to give the system the flexibility to better match your apps icon to the larger icon. In the case of the call UI, that interface is inherently "dark", so the system chose the dark icon.
As an aside here, I'll also note that part of the issue with the dark icon may be that it isn't following one of our recommendations in the Human Interface Guidelines:
"To look at home on the platform, omit the background so the system-provided background can show through."
I know the icons you used are only their to demonstrate the issue, but my broader point here is that you may want to consider designing your dark mode icon with the call UI screen in mind, not just the Home Screen.
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Kevin Elliott
DTS Engineer, CoreOS/Hardware