app/modules/main/templates/cells/generateSortingIcons.html
<span class="hoverSortIcons" ng-if="data.columnSort.sort == false">
<ng-md-icon icon="arrow_forward" size="{{size}}"></ng-md-icon>
</span>
<span class="sortedColumn" ng-if="data.columnSort.sort !== false" ng-class="data.columnSort.sort === ColumnSortDirectionProvider.ASC ? 'ascending' : 'descending'">
<ng-md-icon icon="arrow_forward" size="{{size}}"></ng-md-icon>
</span>