Hmm.. That shouldn't be doing that. Strangeness. Upgrading will fix that though, or it usually does.
If you don't feel like upgrading, then do this.
Go into public_age_check.pl, and find $TBT, it's in the first few lines of the file.
Below it, you'll see something like this:
If that line says anything other than the above code, then change it to the above code. Chances are it in there as $vars_style{TableStripColor} <-- A mistake I've done before while modding my ubb. Or as $vars_style{CategoryColorStrip}. Either of those would give you a grey table bg. More likely the 2nd one though.