[Bug] Shell: Setting Shell.BackgroundColor overrides all colors of TabBar

[KoenMat]

Description

If you specify Shell.BackgroundColor (e.g. Green) without also specifying the TabBar-colors, all TabBar-colors are also green, so all you see is a green TabBar, no icons. If you also specify all Shell.TabBarXxxColors, then it works as expected. In the 'Xanimals'-sample app, this is done rightly with a style. If this isn't a bug, it should be better documented.
This is no problem if you don't specify a Shell.BackgroundColor.
Only tested on Android device.

Steps to Reproduce

1. Take the 'Xanimals'-sample.
2. Remove the references to the styles in every ShellContent-section
3. Put BackgroundColor="Green" in '<Shell' header
4. Run and notice that the bottom TabBar is green and no icons are visible because they are also green.

Expected Behavior

The colors should behave independently

Actual Behavior

TabBar colors all have the same color as set by Shell.BackgroundColor, so no icons visible.

Basic Information

• Version with issue: 4.2.0.709249
• Last known good version: ?
• IDE: Visual Studio 2019
• Android: 8.1.0

[felipebaltazar]

Hello!
Can i work on this issue?