How to reproduce:
1. Create a project with the HDRP package
2. Create a "Lit Graph" Shader (Go to Create>Shader>HDRP>Lit Graph)
3. Double-click the created Graph to open the Shader Graph Editor
4. In the Shader Graph Editor change the "BaseColor" of the Material and inspect if the Main Preview is changing accordingly
5. Create an empty GameObject in the Scene
6. Add a "Static Lighting Sky" Component to the created GameObject and set it to use "ProceduralSky"
7. In the Shader Graph Editor change the "BaseColor" of the Material and inspect the Main Preview

Expected result: Main Preview shows the changed color.
Actual result: Main Preview always shows a fully white color.

Reproducible in: 2019.2.10f1 (6.9.0, 6.9.1)
Not reproducible in: 2019.3.0b7, 2020.1.0a9 (7.1.0, 7.1.2) ("Static Lighting Sky" Component's settings are reworked)

Couldn't test with Unity version: 2017.4.33f1 (No Package Manager), 2018.4.11f1 (No Shader Graph)

Notes:
1. "Static Lighting Sky" Component is available just on HDRP
2. From version 7.1.0, HDRP is reworked in the "Static Lighting Sky" Component's area ("Procedural Sky" is deprecated)
3. From version 7.1.0 use "Sky and Fog Volume" for Sky generation