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

.tablepress .row-hover tr:hover td {
	background-color: #ff0000;
}

If you just want to change this for a specific table, use .tablepress-id-N (with N being the table’s ID) as the selector, instead of .tablepress.