Playing around with it quickly, it needs to be at least that light for the green comment to be legible - otherwise that color would need to change as well (plus maybe others too). Finding contrasting colors that work in all situations can be quite difficult.
I wonder if there's an issue with the forum software actually, as I keep changing this color but it keeps going wrong again a few weeks later. (Either that or it looks VERY different on different screens, and I fix it for one but then it doesn't work on another. I'll look into it when I have a moment.)
Background still seems too bright for a dark theme. And any chances to add alias vbs and js ? I used that in the first post expecting it would work like in GitHub.
I don’t think we have control over the language names. Vbscript and JavaScript both work, and are what you’d need to use on most other Discourse forums as well.