Check Boxes

I am using the GridView widget from Kartik. I want to have a check box or icon in the search menu. By default i get a drop down menu with yes and no. if i add;

[color=#008000]‘filterType’[/color]=>GridView::[color=#660E7A]FILTER_CHECKBOX[/color],[font=arial, verdana, tahoma, sans-serif][size=3] I then loose the drop down menu which is what is good but get a white box instead of a check box. What am i doing wrong[/size][/font]

…GridView::widget([

[color=#008000][b]'dataProvider' [/b][/color]=> [color=#660000]$dataProvider[/color],


[color=#008000][b]'filterModel' [/b][/color]=> [color=#660000]$searchModel[/color],


[color=#008000][b]'columns' [/b][/color]=> [


    [[color=#008000][b]'class' [/b][/color]=> [color=#008000][b]'yii\grid\SerialColumn'[/b][/color]],





    [color=#008000][b]'id'[/b][/color],


    [color=#008000][b]'name'[/b][/color],


    [


        [color=#008000][b]'class' [/b][/color]=> [color=#008000][b]'\kartik\grid\BooleanColumn'[/b][/color],


        [color=#008000][b]'filterType'[/b][/color]=>GridView::[color=#660e7a][b][i]FILTER_CHECKBOX[/i][/b][/color],


        [color=#008000][b]'trueLabel' [/b][/color]=> [color=#008000][b]'Yes'[/b][/color],


        [color=#008000][b]'falseLabel' [/b][/color]=> [color=#008000][b]'No'[/b][/color],


        [color=#008000][b]'value'[/b][/color]=> [color=#008000][b]'mon'[/b][/color],


        [color=#008000][b]'attribute'[/b][/color]=> [color=#008000][b]'mon'[/b][/color],


        [color=#008000][b]'falseIcon' [/b][/color]=> [color=#008000][b]'<span class="label label-danger">Mon</span>'[/b][/color],


        [color=#008000][b]'trueIcon' [/b][/color]=> [color=#008000][b]'<span class="label label-success">Mon</span>'[/b][/color],








    ],.......