How to reproduce:
1. Open attached project "Grayscale.zip" and scene "SampleScene"
2. Observe the two cube GameObjects in Scene window
3. Enter Play Mode
4. Observe the two cube GameObjects in Game window

Expected result: Both cubes are rendered the same
Actual result: The ECS cube is rendered in grayscale

Reproducible with: 2019.3.5f1, 2020.1.0b1, 2020.2.0a2
Could not test with: 2017.4.38f1, 2018.4.19f1 (no URP support)
Reproducible with package versions: 7.1.8, 8.0.1

Notes:
1. Reproducible with Hybrid Renderer versions: 0.1.0-preview, 0.4.0-preview.8
2. Issue does not reproduce with Default renderer
3. Issue could not be tested with HDRP renderer (no Ambient/Gradient in Lighting Settings)