It's very likely that there would be a better and cleaner way, but I'm assuming you are using a foreach to navigate through all the rows, so why not just add a condition?
Excel::create('Report', function($excel) use($clean){
$excel->sheet('Sheet 1', function($sheet) use($clean){
$sheet->row(1, array('Room Attendant Name', 'Room Number', 'Verified'));
$i = 2;
foreach ($clean as $example) {
if($example->col3 == 1){
$sheet->cell('C'.$i, function($color){
$color->setBackground('#008000');
});
}
$sheet->row($i, array($example->relation->name .' '.$example->relation->lastname, $example->col2, $example->col3));
$i++;
}
$sheet->setAutoFilter();
});
})->download('xlsx');
I think something like that should work, but can't assure it at 100% since I don't usually manipulate the style of cells. If you find a better way please let me know since I think in the future I'd probably need it as well.