You are not putting the label "into" the listbox, you are putting the text
into the list box.
Text does not have a concept of colour.
It's actually quite difficult to set the colour of items in a listbox - you could use a ListView instead. Once you have added the item you can change the properties of that item (NB of the item, not the "text")
Or if you really want to use a Listbox you can "draw" the colour yourself - see some suggestions here