rich:dataTable has a headerClass attribute, but I don't believe PrimeFaces has anything equivalent. You could define a style for the <th> row of this table:
I just changed .ui-datatable-header if you wish to change all dataTables. For specific tables, you can use a styleClass attribute for the specific dataTable.
I finished using:
.ui-datatable-header{ background: blue;}
Thanks for your answer !
Don't get me started about those stupid light bulbs.