<meta name="theme-color" content="<a href='/37474'>#37474</a>f"> colors the Navbar in Chrome Android (and Firefox Desktop with VivaldiFox) in the dark grey.
"background_color": "#edecec", "theme_color": "<a href='/37474'>#37474</a>f",
cause the splash screen of the webapp on Android to have the same background and navbar color as Piwik.
Adding a higher resolution icon to
<link rel="icon" /> (probably) causes Firefox to show the large logo on the new tab site in Firefox 47+ (which is quite a mystery)
Thanks for the nice PR @Findus23 - this will be deployed on demo.matomo.org in the next few hours