Repro Steps:

1) Create a Project with a MainPage.xaml
2) Introduce a Button Element to the Stage of MainPage.xaml
3) In the TabControl's Properties, change the Background Property to any other Solid Colour brush, and exit the Colour Picker.
4) Press Ctrl+Z to return to the previous colour that came with the Template.

Observe how no changes take effect.

5) Select another Colour from the Colour Picker and exit it.
6) Press Ctrl+Z to return to the colour selected in Step 3).

Observe how no changes take effect.

Expected Result:
Undoing a Colour Selection returns the Property to the Previous Colour