As agreed in PR 6301, preview releases should have a different icon to distinguish it from the production version and avoid people accidentally using the preview version.
For the daily builds I already changed it using the code here to use the Powershell_av_colors.ico icon:

The only remaining icon is Powershell_avatar.ico:

Therefore I suggest that the preview should use the Powershell_av_colors.ico icon instead now and the daily builds should start using the Powershell_avatar.ico icon instead.

I think, preview builds (produced e.g. by AppVeyor) should also have a different icon and I will leave it up to the maintainers which of the 2 icons to choose or if a new icon should be used for those.