On Quickbar and icons…
Selecting the default icon for an app on the Quickbar is a bit complicated™. Some apps will use their notification icon if it can be found. Unfortunately there’s no API to fetch this icon, so it can be unreliable. Sometimes the resulting icon can also be a little low-resolution, but generally it’s pretty good.
Many particularly well known apps will automatically be assigned appropriate icons, but failing that you can pick from any of Google’s Material Design related icons that have been bundled with the app.
At this time, a conscious decision has been made to not allow colored app icons on the search box/action bar, to best match the Material Design guidelines. This decision may be revisited down the road.
Currently, icons on the search box/action bar are aligned to the right. Some people may want to use a method of centering items evenly, which isn’t currently supported, but may or may not be added in a future update.