How to reproduce:
1. Create a new Unity Project
2. In the project window, right-click -> Create -> Shader Graph -> Blank Shader Graph and open it
3. In the Blackboard, click the "+" sign and add the "Color" property
4. Open the created property in the Graph Inspector and click on the "Default Value" 
5. Observe the Alpha slider

Expected results: Alpha is set to 100
Actual results: Alpha is set to 0

Reproducible with: 2022.3.56f1, 6000.0.34f1, 6000.1.0b2

Reproducible on: macOS Sequoia 15.1 (M1)
Not reproducible on: No other environement tested