You can use datepicker (jqueryui) options using opts param.
http://api.jqueryui.com/datepicker/#option-firstDay

"opts" => array("firstDay" => 1)

$col["formatoptions"] = array("srcformat"=>'Y-m-d',"newformat"=>'d.m.Y', "opts" => array("firstDay" => 1));

I wanted to change my start day to Sunday, so I change 1 for 0 and it works.. However, the search bar at the top of the column won't filter the day I select. If I take this line out it will work properly but the start day is back to Monday.

$col["formatoptions"] = array("opts" => array("firstDay" => 0);

Hello,

I am unable to regenerate this case. I used this formatoptions and working as expected.
$col["formatoptions"] = array("srcformat"=>'Y-m-d',"newformat"=>'Y-m-d', "opts" => array("firstDay" => 0));