Right click a sheet and choose Name and Comments… to set sheet color.
Select sheet in Object manager and use Sheet Comments button on mini toolbar to set color.
When a workbook/matrix book is active, and nothing is selected, click the Fill Color toolbar button can change sheet tab color now. Set color by Labtalk command, e.g.
wks.tabcolor=color(128, 128, 0);
Sheet tab color also shows in Object Manager.
Right click sheet and choose Comments mini toolbar button to change sheet tab color and comments.