Yay for new koi! But I have a few questions...
1) Is the tank cycled? They are very sensitive to water quality and can develop major problems if the tank isn't "perfect".
2) What's the filtration in the tank?
3) Are there hiding places for the koi?
4) Is the tank covered? They are strong jumpers and even though they can live out of water for a short time, that's not recommended....lol
5) How big is the pond? It is recommended like 1,000gal's for the first koi & 500 each additional one...they may not have the biggest bioload[mine are cleaner then my goldfish] but they get to be 3' long.
Answering your question; I believe Fishman is correct...they are just adjusting and won't just yet.
Also, moving to the pond is going to be a shock to them from going to a warmish, covered, filtered, aquarium where they are feed "in peace" to having to fight basically for their lives outside; so they will be shy for the first probably...year...lol Mine are like 2 now[1' and in a way too small pond soon to be upgraded] & really still want nothing to do with me when it's not feeding time. Unlike the goldfish, they actually recognize me; so they are personable.
Good luck with them!