As far as i can tell this it another thing related to 32bit apps and not having support for it from windows. There does seem to be some ways to do make dark colors work but none of them are official and all seem unsupported by windows.
I will post some links here to what i found for any others interested and more experienced than myself with these things, In the hope some one can make more sense out of it.
From what i read i do not think this will be done on Fusion 2.5 32bit. Maybe some one can offer more of a solution or share ways of forcing the whole GUI to be dark. Im not really a fan of adding third party apps to windows to change things but for Fusion i might make an exception if there is a recommended free and stable way of doing it. I only really use a windows pc for Fusion anyway every thing else i use Mac.
Thanks to any one that can help with this.