SUMMARY
If I try to change the color of the Gamut Warning by setting the RGB color to 128,128,128 in Settings > Configure Krita > Color Management > Soft Proofing, as soon as I click OK and close the settings window, the color reverts to the default, which is solid green 0 255 0.
If I go back to the settings, I find that the color is set to 0 255 0. No matter what color I choose, Krita ignores it. I even manually set “defaultProofingGamutwarning=128,128,128” in the kritarc file, but the problem remains. After restarting Krita, the setting automatically reverts to “defaultProofingGamutwarning=0,255,0.”

STEPS TO REPRODUCE
1. Open a project with AdobeRGB color profile
2. Settings > Configure Krita > Color Management > Soft Proofing > set Profile to sRGB IEC61966-2.1 
3. Settings > Configure Krita > Color Management > Soft Proofing > Gamut Warning set to 128,128,128
4. Click OK
5. View > enable "Soft Proofing"
6. View > enable "Gamut Warning"

OBSERVED RESULT
The image areas outside the gamut indicated by the gamut warning are still pure green 0, 255, 0.

EXPECTED RESULT
The image areas outside the gamut indicated by the gamut warning aregray 128, 128, 128.

SOFTWARE/OS VERSIONS
WIndows 11 25H2 Build 26200.7171