Pleasing everyone is not an easy task for sure 
For me most of the internal subtitles are still too bright. But since I rarely use PGS subs (the font is too big for my taste, I know, I’m picky) I came up with my own solution:
I only use external subtitles and add <font color="#676767"> to every line. The Plex plugin/channel Sub-Zero Subtitles does it automagically for me (after a small change to the python script), so there’s very little or no effort involved.
If anyone is using Plex with Sub Zero, the colour codes for subtitles are in the file
Plex Media Server\Plug-ins\Sub-Zero.bundle\Contents\Libraries\Shared\subzero\modification\mods\color.py