I'm not certain what the specific cause or set up that causes this, but it appears that when an Colour is changed within Style/Template, it cannot be undone.

Repro Steps:

1) Open the WorldUI_Unity Demo from the InternalProjectsGitHub by opening \WorldUI_UnityDemo\Assets\WorldUI\WorldUI.noesis in Studio.
On the Stage, the ObjectPanel xaml will be opened.

2) Right click on the section where the orange 'info' button is located, and navigate to Templates/Button/Edit Current
This will open the Template within the Style.

3) From the Navigator, select the Element named 'RingButtonPath', and from its Properties Panel, change its 'Fill' colour to any other colour, then exit the Colour Picker Panel.

4) Click anywhere on the Stage not taken up by an Element, then press Ctrl+Z.

Observe how the Colour change performed in Step 3) does not revert.

5) Close ObjectPanel.xaml, then re-open it.

Observe how the colour has now been reverted as expected.

Expected Results: The Undo/Redo system on-Stage displays the changes undone or redone.