I recently got a nearly unused TVOne CS-450 off eBay, and it's worked great. However, I did have one main issue, and that's that the complete removal of black makes the text hard to read in many cases

^ Screenshot for how they look when I sync in AegiSub

^ How they look during playback
Is there any way to change the color the genlock removes? This is more of a readability issue honestly, and if that's not possible I'm fine with that

Ugh I was just thinking about trying to buy another one of these in the hopes it would work but then decided I have too much stuff I need to focus on selling off
so I'll skip the genlock for a few more years.

Sorry I can't help.

Just change the shadow color of the font from black to example white or anything you like, then the visibility will be as good as before.
You can also increase the font size if you feel the subtitles are hard to read.

Updating this: after some testing with mspaint I found that the CS-450 stops removing the outline at around luma 80 on the color wheel; changed my scripts to use that color as a outline and it's much easier to read now