First of all, there is no such thing as 'black U' with USDT. No matter which chain's USDT contract you are using, its protocol does not have the function to 'black out' USDT. Therefore, USDT will never be suddenly 'blacked out', so rest assured!
So, what is a 'black money wallet'? In fact, this situation could happen. If your wallet address is frozen by an exchange, or if it is frozen by the FBI like in the Tornado incident, then you will be in trouble. You cannot directly transfer these USDT to the exchange for trading. However, decentralized wallets are completely free from these restrictions, and you can still transfer freely, unaffected! This is the charm of decentralization—completely unbound by any centralized institutions!
Technically speaking, transactions on the blockchain are public and transparent, and each transfer is broadcasted. Therefore, if your wallet is frozen, as long as you transfer the frozen funds to a wallet that isn't frozen, the exchange can see the correlation of the transactions and may freeze all related addresses. In other words, if all transfers were 'black', wouldn't that make the work of underground money houses pointless? This operation is clearly unrealistic!
To summarize, USDT won't be 'black', the only thing that could possibly be 'black' is the wallet address—specifically, the wallet address you are transferring from. If you receive a transfer from a 'black' wallet, don't panic; usually, there is no problem. Unless your wallet itself is having issues.
So, there is no need to worry about USDT becoming 'black U'. As long as your wallet is fine, USDT is your USDT, safe and reliable!