The way to disable a listbox item is to prefix the list entry with a \ character. For example:-

ThisForm.ListBox.AddItem("\Disabled")
ThisForm.ListBox.AddItem("Enabled")

The ItemBackColor property can be used to change the background colour of an item but I don't think you can do this on an entry by entry basis. For example:-

ThisForm.ListBox.ItemBackColor = RGB(255, 255, 255)