You should move it back when KDE is not running. The settings might not be read back immediately and even be overwritten again with the current (default) ones.
And please note that KDE (or any KDE application) will re-create the folder automatically. So you might have moved the old .kde4 folder inside the new one by mistake, so it may be ~/.kde4/.kde4/ now which is ignored of course. (this can happen when you use “mv .kde4.old .kde4” inside of KDE4 f.e., it has happened to me already… 
)
So we can conclude that it
was something in the kde4 directory, but what?
Well, I can only guess here. But probably some setting related to the colorscheme, style, or theme.
You could move back the configuration files one by one (or in batches) to find out which one caused it.
No idea whether it’s worth the bother though.
