Steps to reproduce:
1. Open the attached project “KeywordBug“
2. Select the “Assets/Mat.mat“ Material
3. Set the Shader to “Assets/TestUnlit.shader“
4. Change the Inspector window mode to Normal (click the “3 dots” icon next to the “lock“ icon)
5. Enable the “Use Color 2“ option
6. Change the Inspector window mode to Debug
7. COLOR2 is listed in the Valid Keywords list
8. Change the Inspector window mode to Normal
9. Modify the Color2 color
10. Change the Inspector window mode to Debug
11. Observe the Valid Keywords list

Expected result: COLOR2 is listed under Valid Keywords
Actual result: COLOR2 is not listed under Valid Keywords, despite the "Use Color 2" toggle being on

Reproducible with: 2021.2.18f1, 2021.2.19f1, 2021.3.17f1, 2022.2.5f1, 2023.1.0b3, 2023.2.0a1
Not reproducible with: 2020.3.45f1, 2021.2.17f1

Reproducible on: Windows 10

Notes:
1. Material color reverts to “Color“ when pressing CTRL + S after step 8
2. Look at the attached video for clarity