Reproduction steps:
1. Open the project attached by the user
2. In the Project window, select the "New UXML Template" Visual Tree Asset
3. In the Inspector, click Open
4. In the UI Builder Hierarchy, select the Image (NewUXMLTemplate.uxml > VisualElement > VisualElement > Image)
5. In the UI Builder Inspector, navigate to the Border section
6. Note that the Color is (0, 0, 0, 255) and the Width is 1 pixel
7. Observe the Image in the UI Builder Viewport

Expected result: The Image has a 1-pixel black border
Actual result: The Image border is invisible because the default color alpha is shown as 255 but rendered as 0

Reproducible with: 1.0.0-preview.15 (2019.4.30f1), 1.0.0-preview.16 (2020.3.17f1, 2021.1.19f1, 2021.2.0b9, 2022.1.0a6)