How can I change the colors of the table head row?

This can be done with the some CSS code that needs to be added to the “Custom CSS” textarea on the “Plugin Options” screen of TablePress:

.tablepress thead th,
.tablepress tfoot th {
  background-color: #ff0000;
  color: #00ff00;
}

To also change the hover color when sorting, and the background color of the column that is currently sorted, add

.tablepress thead .sorting_asc,
.tablepress thead .sorting_desc,
.tablepress thead .sorting:hover {
  background-color: #00ff00;
  color: #00ff00;
}

You can change both the text color (via the color property) and the background color (via the background-color property).

TablePress