With DHTMLX 4.2.1 (at office so not very new so I would have loved snippet to work to test against last stable version) I noticed the following bug:
When ignore_timeline function filters displayed hours, tree mode displays one empty TD cell of width 0px or 1px, for every filtered hour, but only for tree section title row, in my snippet the “Production Department” and “Sales and Marketing” lines. So the sections title lines will have extra blank space.
Interesting, I tried your solution but there is a very tiny visual glitch, the TDs are now in right color but there is an extra pixel at bottom of the TD. All the TDs have no border nor margin.
/* scheduler timeline view in tree mode */
.dhx_data_table.folder .dhx_matrix_cell, .dhx_data_table.folder td, .dhx_matrix_scell.folder {
background-color: #067FB8;
color: white;
}