Sometimes Desktop and Taskbar icons get 'messed up'. They go 'white'. It seems to happen mostly in environments using Roaming Profiles and Redirected Folders. Environments we use 100% of the time.

If the shortcut icon exists and is 'messed up':

Right-click → delete the problem icon

then

Locate or Search for apps in the Start Menu (Metro) → right-click The app icon → Pin to Desktop

I've found the Task Bar icons to be particularly flaky and the reason is not overly obvious. I think they probably work fine in simple, non-roaming profile, non-redirected folders environments.

In my case, I avoid using Task Bar icons…mostly. If I deem it 'worth it', I just delete them and recreate them when they 'flake out'.

Right-click → delete the problem icon

then

Run the app → right-click → pin to Task Bar