Currently, in the Resources Panel, the order of Resources for any given ResourceDictionary are manually ordered.

However, there appears to be quite a degree of unpredictability in how the same Resources are displayed in the 'ResourceDictionary Stage Preview' document.

See repro steps for such an example.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml

2) Navigate to the Resources Tab, and select GlobalResources.

3) Using the '+' icon in the top right of the Resources Panel, create the following, in this order:
--> x1 Color Resource, set to any colour.
--> x1 Color Resource, set to any colour.
--> x1 ControlTemplate , set as a 'Button' Target Type.
Do not rename any of these yet.

4) Navigate to the GlobalResources.xaml tab at the top of the app to expose these Resources in the Resource Preview Mode on-Stage.
Observe how the order of the Resources on-Stage does not match the order set in the Resources Panel, and appears to be on-Stage in Alphabetical order. (This isn't necessarily an issue in itself.)

5) Rename 'Color.001' to 'A'
6) Rename 'Color.002' to 'B'
7) Rename 'ControlTemplate.001' to 'C'

Observe how the order of Resources on-Stage have shifted around to now be in Alphabetical order according to the new names of the Resources. Once again, no particular issue here.

8) Using the 'dragger' in the Resources Panel, re-arrange the resources in the list, to change their order from 'A, B, C' to 'C, B, A'.
Observe how the order of Resources on-Stage has not changed. No issue here.

9) Save, then close the GlobalResources tab, then re-open it.

Observe how now the order of Resources on-Stage now displays as 'C, A, B', which corresponds nor to an the Alphabetical ordering observed in Step 8), nor to the manual ordering of the Resources in the Resources Panel.

Expected Results: Resources on-Stage in the Resource Preview Mode display in some discernible pattern. (Just as a personal note, I think that setting them in the same order as they are in the Resources Panel would be the ideal UX, but Alphabetical would be acceptable too.)
Expected Results: Resources on-Stage in the Resource Preview Mode display identically between before and after the GlobalResources.xaml tab is closed and re-opened.