How to reproduce:
1. Open the attached user project “1510509 SpriteThumbnail.zip“
2. Open the “UI-Custom“ shader
3. Change the color of the shader by commenting line 57 in the shader
4. Expand the “Test_atlas 1“ Texture and select the “Test_atlas_0“ Sprite

Expected result: The color of the Sprite is the same in the thumbnail and in the Inspector preview
Actual result: The color of the Sprite is different in the thumbnail and in the Inspector preview

Reproducible with: 2021.3.27f1, 2022.3.3f1, 2023.1.1f1, 2023.2.0a21

Reproduced on: macOS 13.4 (Intel), Windows 10 (by reporter)

Notes:
- The thumbnail can be updated through Script (by opening the “ForcePreview” window (Window > UI Toolkit > ForcePreview), copying the mentioned Sprite path, pasting it into the “Asset Path” text field, and pressing “Force Preview“), but only if the Editor is restarted
- On the newer versions, the color is updated when the Editor is restarted