I don't think its necessary.
While some people may not be able to see the button, 95% of the people out there are able to see it (supported by how many new questions we get in any given time period greater than an hour). Given this, I wouldn't find any supportlogical reason to change the way it is now.
As well...
A single grey / translucent back background should fix the problem
That would take away from the design of the site. Aesthetics are important, and adding a grey or translucent background to the button takes away from the aesthetics (it looks ugly).