Define each style of the down arrows.
<style type="text/css">
.mb1 .m-btn-downarrow{
background-image: none;
}
.mb1 .m-btn-downarrow:after{
content: '';
display: block;
position: absolute;
width: 0;
height: 0;
border-style: solid;
border-width: 4px;
border-color: transparent;
border-top-color: teal;
top: 50%;
left: 50%;
margin-top: -2px;
margin-left: -4px;
}
.mb2 .m-btn-downarrow{
background-image: none;
}
.mb2 .m-btn-downarrow:after{
content: '';
display: block;
position: absolute;
width: 0;
height: 0;
border-style: solid;
border-width: 4px;
border-color: transparent;
border-top-color: red;
top: 50%;
left: 50%;
margin-top: -2px;
margin-left: -4px;
}
</style>
Add the menubutton css class to change the down arrow style.
$('#b1').addClass('mb1');
$('#b1').addClass('mb2');