Originally Posted by
Peregrine415
Any reason why not use your US passport. Colombia does not require visas for US passport holders.
I'm a US citizen who lives in Colombia. The poster is correct that no visa is required for visitors holding US passports.
That said, the passport used at immigration must be the same on entry and exit. Immigration needs to match the entry to the exit. They would have no interest in your US passport if you entered with your UK passport. They also don't care which is registered with the airline - that is only of interest to your destination country.
In my case, my kids are dual citizens. They use their Colombian passports at immigration in Colombia, but their US passports are listed with the airline.