IPR/Progressive doesn't respect 'affect background' in color mapping rollout.

[Pixelcon]

Titles explains it all.

IPR and/or progressive production mode renders background with a much different brightness level compared to bucket mode.

Max 2023. Vray 6 hotfix 3

Simple jpg loaded as such:

[hermit.crab]

It's expected; there should be a warning in the log about this. You can disable the "Force progressive sampling" in the IPR options (Bucket sampler must be active) to preview the effect, though.