Text disappears in UI Builder when Outline Width is increased due to Outline Color defaulting to alpha 0

Steps to reproduce:

1. Create a new URP project
2. Create a new UI Document and open it in UI Builder
3. Add any element to UI Builder Hierarchy, e.g. Label
4. In the Hierarchy, expand "Text" foldout and "Text Effects" foldout
5. In the "Outline Width" property increase the value to 1 or 2
6. Observe the Label text disappears
7. Open the "Outline Width" color picker
8. Observe the Alpha field

Actual results: Increasing Outline Width makes the text disappear because the default Outline Color alpha is 0

Expected results: Outline Color should not default to alpha 0 and increasing Outline Width should keep the text visible with thicker outline

Reproducible with versions: 2023.1.0a4, 6000.3.14f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a4

Tested on (OS): macOS 26.4

Notes:

• Other color properties do not default to alpha 0