decorating dropdown list box text?

I'm displaying the sizes and prices of items in a dropdown listbox, something like this:
Bar - $6.00
Whan an item is on sale, I want the retail price to be displayed with a line through it, and with the sale price next to it in green.  Like this:
Bar - $6.00 $5.40
So far, I've only experimented with the line through.  I tried this:
Dim sTest As String = p.size & " - <span style='text-decoration: line-through;'>" & FormatCurrency(mSoldPrice) & "</span>"
newListItem = New ListItem(sTest, p.prodDetailID)
The entire span tag gets displayed.  Is there a way to do what I want to do?
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