Reproduces on all versions of Shadergraph with the Sprite Lit and Unlit shadergraphs (6.9.1, 7.0.1, 7.1.1 and Github Master 8.0.0 (eca116d0f3))

Repro steps:
1. Use a project with Universal RP
2. Create a new Sprite Unlit shadergraph, and open it
3. Change the color input to the master node to red, without creating a color node input

Expected result: the preview is red
Actual result: the preview is yellow

Notes: This only affects the preview in Shadergraph. Materials with the shader in the material preview and the scene will be the correct color.
This only affects setting the color directly on the master node. Sampled and inline colors and textures will preview correctly.