Feedback from installing on various Windows PCs. (This post will keep getting up dated with other findings as I run on other PCs)
Win10 Pro (x86) PC first.
Missing icon at install time
During install I ticked “Start menu”, “Desktop” and “Taskbar” icons. Only the first two appeared - no icon was added to the taskbar.
Do I assume you are not automatically pinning a Tile to the Start Menu? Just adding to the normal A to Z list of applications.
Start Menu Tile
Funnily enough, when I pinned up the Tile to the Start Menu it fitted this PC almost perfectly as it is a very very similar shard of violet. 
Still think that transparent would be better as it allows more choice for the user.
BUG IN THE INSTALLER
Found my first show stopper of an issue. Why does the installer not warn that this is a 64-bit app? I happened to pick a 32-bit Win10 PC to test on. The installer ran right through to the end, and only when I tried to run the application did I get told it was not compatible.
The “Is this a 64-bit PC?” test should really happen in the installer.
(I think I remember something saying there will be no 32-bit release. So this Win10 PC is now abandoned from this test)
Test of uninstaller
This passed with flying colours. No traces left after uninstallation.
-=-=-=-
Vista Home Premium (x64)
Ahhh… the ever lovely Windows Vista. Everyone’s favourite OS…
Missing icon at install time
This time all three did appear. The Quicklaunch\taskbar icons is present this time.
Launch Application fails - Error Loading Python
Message box appears:
Error loading Python DLL: C:\Program Files\MusicBrainz\Picard\python37.dll
LoadLibrary: A dynamic link library (DLL) initialization routine has failed
Should the Picard installer have installed the relevant Python libraries? I remember this coming up a few months back but the implication there was this should work on Vista x64. (Python 3.7 claims to still work on Vista)
Rebooting made no difference. Let me know what else to check here.
(More tests to follow…)