While it is true that black text with a grey background is just about ideal for the most common reading conditions, changelogs are almost always short enough that it's probably not relevant. Any way you look at it, there's no evidence that the strain of what we're going to call 'sub-optimal' reading conditions causes any long term issues. If it's an easy fix, awesome. I'm not really concerned about it though.
I actually misread your initial post. No don't do this.
A light grey background with black text (the current setup) is generally pretty close to ideal for eye strain in reasonable lighting. In dark rooms, a black background with light grey text can be preferable to reduce eye strain.
Why the forums use a dark grey background with white text? All sorts of reasons. Maybe just a bad choice? Probably because it doesn't matter all that much either way. Eye strain is just the result of the muscles in the eye working, like how you can get sore muscles from hard day of physical labor. No permanent damage. It's just a matter of comfort.