Reproduction steps:
1. Open the attached “AnimateColorMaterialBlockBug“ project
2. Open the “Assets/TestScenario/SampleScene“ Scene
3. In the Hierarchy window, select “SpriteRenderer“ GameObject
4. In the Inspector window, make sure “Overwrite Color“ and “Overwrite Saturation” options in “Set Material Property Block” Script are enabled
5. Enter Play Mode
6. Observe the Game View and wait until the Image starts to fade

Expected result: The image stays red when fading
Actual result: The image turns to white before fading

Reproducible with: 6000.0.42f1, 6000.0.54f1, 6000.1.12f1, 6000.2.0b10, 6000.3.0a2
Not reproducible with: 2022.3.65f1, 6000.0.41f1

Reproducible on: macOS Sequoia 15.5 (M1 Max), Windows 11
Not reproducible on: No other environments tested