You could have a p2p USD or EUR derivatives. Suppose someone colors a satoshi and assigns a one dollar face value to it, promising to exchange this Satoshi for one USD of bitcoins in the future at the current bitcoin/USD market price. Suppose colored bitcoins and regular bitcoins can be traded via a p2p exchange.
Yes, but you still need trust. Existing exchange could issue USD deposits certificates by coloring satoshis and users will be happy to hold the proof themselves while still having to trust the company, not for the exchange anymore, which is conducted in the blockchain with colored coins, but for the deposits. Users should still be able to withdraw the paper by sending their usdCoins back to the issuer.
Why would a company do this?
Bonds, IOUs, future contracts, currencies, vouchers, tickets, ETFs, discounts, smart property, votes, certificate of deposit, academic certificates, property registry, beer tokens and poker tabs with friends.
The question is, why would a company want to use another technology for anti-counterfeiting?
You may need more privacy than what can the chain can offer, which I think will be enough for most if not for all with hardcore obfuscation. Maybe it's about the confirmation time.
The ripple protocol solves this same problem in a different way that is stronger in these two points, but there's many cases in which the public accounting is actually a feature. You don't need the issuer online to move the asset, the chain signs the movement for him. For the smart car property example, you want to be able to sell it even if the company that sold it to you goes broke.
I hope that there can be more coin colors than people (everybody issues, but only your neighbors accept yours, so you ripple your satoshi to pay). I don't think all of us will have our own server always online. So we will need to trust a ripple server for the assets we issue or just use the chain.
I think of these as possible long-term goals for this project. A BTC/LTC exchange would be a good starting point.
A BTC/LTC is feasible but requires changes in the current protocol (enable nLockTime and transaction replacement), but colored coins don't.
Maybe we have the p2p fiat/coin exchange than the p2p coin/coin after all.
I remember when I writed about exchangeCoin, which was a protocol which listened to other protocols to enable atomic exchanges with it. Other chains could do the same to be tradeable for others apart than from exchangeCoins. Now that I think about it...what a stupid idea I had then.