Hi 

You can set the style of the column dynamically by using  setStyle 

Below is the code snippet :

HtmlColumn firstNameColumn = new HtmlColumn ();
firstNameColumn.setSortBy("firstName");
UnifiedOutput columnFirstNameHeader = new UnifiedOutput();
columnFirstNameHeader.setValue("FirstName");
firstNameColumn.setHeader(columnFirstNameHeader);
UnifiedOutput columnText = new UnifiedOutput();
UnifiedValueExpression uniValueExpressionFirstName = UnificationHelper.createUnifiedValueExpression(context,"#{DATA_ROW.firstName}");
columnText.setUnifiedValueExpression("value", uniValueExpressionFirstName);
firstNameColumn.getChildren().add(columnText); 
firstNameColumn.setStyle("background-color: #e6e6e6; text-overflow:ellipsis; overflow:hidden; white-space:nowrap; width:100px; "); 
grid.getTemplateItems().add(firstNameColumn);