Have you tried

$('#cboxWrapper', context).css('backgroundColor', bg);

It makes sure your css is ran with the new markup Or checked that your selector actually works  ?

console.log($('#cboxWrapper')); // Then check your console

Have you tried using context?

$('#cboxWrapper', context).css('backgroundColor', bg);

It makes sure your CSS is ran with the new markup.

Did you check that your selector actually works?

console.log($('#cboxWrapper')); // Then check your console