Let put is simply: Who is the owner of the site? ----> Memblers. I think he has a right into it. The color scheme/logo as been there for a while and is part of the site identity. It's nothing to do about readability or things like that.
If he's fine with the normal wiki color and approve it then I don't need to research more on how to apply any CSS. The color scheme is for the nesdev page part only, not the wiki.
edit:
I will answer the question. I didn't want to answer first since it could be seen as flame but it shouldn't be seen that way.
1. Reason is mentioned above. Memblers is the owner so he has the right to take the final answer on what he likes or not. If he like the wiki standard color for the nesdev front page then let it be.
2. This can be subjective. Personnaly, I'm fine either way. Like some people prefer clear type and other people hate it like hell.
3. Nesdev is a very, very niche site so you shouldn't worry too much about that
4. My time would be better spent on my own project
As long as it doesn't take me 2 month, I don't mind to spend a little bit of time to install 1 plug-in and make 1 CSS to overwrite the page content of the nesdev front page only if it helps Memblers. That site wouldn't exist in the first place if Memblers wasn't there.
5. Extension of #4. I don't mind to spend a little bit of time for helping Memblers. I don't want to spend too much time on it thought.
This is my only intention. If Memblers prefer a lime background with pink dot, even if doesn't make it readable then so be it. I may complain a little bit thought
But right now the color scheme is not that bad but I mentioned that I don't want to apply it to the main wiki content. The plug-in, if it does work properly in the first place, allow you to apply a CSS to a specific page only. If it doesn't work then I will drop it and Tell memblers "no can do", that's it.