Just use GUICtrlSetBkColor()
Global $GUI = GUICreate("Multi-Colored Listview", 500, 500)
Global $list_view = GUICtrlCreateListView("Item #|Color", 5, 5, 490, 490)
Global $colors[5] = [0x00FF00, 0xFFFFFF, 0xFFFF00, 0xFF0000, 0x0000FF]
For $x = 0 To 4
GUICtrlCreateListViewItem($x & "|" & Hex($colors[$x], 6), $list_view)
GUICtrlSetBkColor(-1, $colors[$x]) ;replace $colors[$x] with the RGB color code you want to use
Next
GUISetState()
While GUIGetMsg() <> -3 ;$GUI_EVENT_CLOSE
WEnd