Example:

//Instantiating a Workbook object
Workbook workbook = new Workbook();

//Obtaining the reference of the first worksheet
Worksheet worksheet = workbook.getWorksheets().get(0);

//Add new Style to Workbook
Style style = workbook.getStyles().get(workbook.getStyles().add());

//Setting the background color to Blue
style.setBackgroundColor(Color.getBlue());

//Setting the foreground color to Red
style.setForegroundColor(Color.getRed());

//setting Background Pattern
style.setPattern(BackgroundType.DIAGONAL_STRIPE);

//New Style Flag
StyleFlag styleFlag = new StyleFlag();

//Set All Styles
styleFlag.setAll(true);

//Get first Column
Column column = worksheet.getCells().getColumns().get(0);

//Apply Style to first Column
column.applyStyle(style, styleFlag);

//Saving the Excel file
workbook.save("D:\\book1.xls");