Personally, I think that the grey box sitting against the background image itself is a huge, huge no-no in terms of graphic design. Think of it like cutoff in levels, for example, do we have just a dirt block, or do we have a dirt block with something to go with it? Is that cave tile going to sit there, or are we going to put the crystal border blocks around it?
The same can be applied here. The theme is a level, the background gradient is our background, and everything sitting against it is either cutoff or a decoration block/item of some sort. However, our little decoration blocks don't have something to keep them from clashing, such as a border, a shadow effect, or a shaped outline. Instead, we have a dark grey box just saying "hey look at me, I have no visible outline.
I'll use
Minecraft Forums as an example. Notice how their header bar(not the Curse one) has a 3D effect, and how their forums block has a CSS shadow to keep it away from the blue and green. When the background transitions to a blackish grey, it loses the shadow/becomes less visible, and you are left with a light grey/white. In graphics and web design, this is appealing, as you don't have a pure white on a pure black, which is easier on the eyes, but rather you have a lighter black behind a greyish white.
That's not really what we have here. We have dark grey on light blue. That wouldn't be a problem, but nothing keeps the two from clashing. It's practically like putting red walls with blue carpet and not having a purple trimwork to separate them.
Another unsettling factor is this. This should NOT be a thing. At all. A separate divided container if anything, but when it just sits against the background, it makes it harder to see. And if that doesn't clarify my point,
this and
this Can you read that without changing your screen brightness or tilting your monitor? Do you think a user should have to see that? "But no one looks at that" It doesn't matter, it's still an underlying problem that can either be tethered or related to another graphical issue.
Here is an example of what I did on reddit. If altered and applied to our theme, it would work well, with a light grey 2px border, or using the header-bg image on the other sections of the site, such as posts, post reply pages, and thread backgrounds on the main sections of forums.
This however is not a good design scheme, if unbordered. That is my main pet peeve. Our header background would look better if rounded borders were applied to give it a 3D effect, and would help the header stand out more.
That's just my point of view.
Edit: Maybe brighten up the hue on link colors too? Or have posts have a lighter grey when hovered. Little tricks like that, you know? Those help tremendously.
Edit2:
by settled I mean I thought we were implementing both the light and dark version and letting users toggle them at will
Sadly, no, we only discussed that, and it never became a thing, because apparently everyone likes the dark theme, or we thought people needed to get used to it. I don't even know, but that option was never given.
Also why do we still have the onsite chat frame if we're not ever going to use it?