[BUG] DVD Subtitles Color and Aspect Ratio Problems

[Selur]

Again no details.
You should know better. So it's wild guessing again,...

Also they start to look less contrast probably due some incorrect PC-TV Levels transformation:

Since Hybrid does not do any tv<>pc levels transformation unless you tell it to it sounds more like the content isn't properly flagged.
-> Check your encoding settings and adjust the pc<>level flags.
Hybrid also supports the ColorMatrix filter which would allow PC<>TV level transformations.

About subtitles:
If you embed the subtitles, the Vapoursynth/Avisynth Preview should help you to see what is happening with the subtitles.
Depending on the position of the subtitles and resizers you might distort the subtiles.

If you tell Hybrid to extract&add the subtitles that is what it will do, it will simply extracts the subtitles from the source and then muxes them back.
Hybrid does not change the subtitles, if you want to change the resolution the subtitles are based on you need to adjust the subtitles.
Read up on the .idx/.sub format (https://wiki.multimedia.cx/index.php?title=VOBsub).
There are some parameters that might be interessting to you like 'size', 'scale'.
Hybrid has currently no option to adjust subtitles when extracting and muxing them.

Do you think it is possible somehow fix these problems?

No details, no clue what you do: No.

Cu Selur