Add a variable for IMAGE SUBS COLOR and/or LUMINANCE when using Nvidia RTX Video HDR

Expected behavior of the wanted feature

Hello. I wasn't sure if this is a bug or just something mpv doesn't know how to do yet but after experimenting with various settings I figured it might just be a new feature request.

First, I added this to my config to engage Nvidia RTX Video HDR:
vf-pre=d3d11vpp=nvidia-true-hdr

If I use SRT subtitles all is well. Their color can be changed via 'sub-color'.

But when I now turn on PGS subtitles for any SDR video file I try, none of the solutions to change subtitle colors work anymore.

The SDR method of changing SRT color "sub-color = 0.8/0.8/0.8/1.0" doesn't do anything. Expected, it shouldn't affect PGS subtitles.
Neither does "sub-hdr-peak=140" work. Expected, it shouldn't affect PGS subtitles.
But then, not even does "image-subs-hdr-peak=1500" work. THIS is the problem right here I think.

Curiously, when I change Nvidia App's Video HDR settings like max luminance or middle grey nits, the video is impacted as expected but overlaying PGS subtitles are still as bright as a white sun regardless of how low I set the values to.

This makes me think MPV isn't passing the PGS subtitles to Nvidia's Video HDR and instead renders them on top somehow, but there seems to be no way to make these PGS subtitles any less bright than "BURN YOUR EYES" bright, because no variable seems to affect these PGS subtitles.

Am I missing some obscure setting that would control PGS subtitle brightness before its overlayed on top of RTX Video HDR output, or is this a genuinely missing feature?

Thank you for your attention!

Alternative behavior of the wanted feature

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Log File

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Sample Files

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Start by reproducing the issue with vf-pre=d3d11vpp=nvidia-true-hdr, PGS subtitles, and an SDR video, then trace how image subtitles are handled relative to image-subs-hdr-peak. Compare that path with the existing sub-color and sub-hdr-peak settings; done means a configurable image-subtitle color or luminance control affects PGS subtitles under RTX Video HDR.