USDT is a token whose supply is controlled by the third party company Tether. I said token, because I want to emphasize that it differs little from colored bitcoin. The Lightning Network is not a sidechain, wherein outputs can be colorized, and therefore any unit beyond the original can't be transmitted.

To give an example. If a user pays a Lightning invoice, he may own colored coins, but the payment isn't usually made with his money, but with intermediary nodes who pay each other until it reaches the final destination (see onion routing).