I would consult a lawyer. Does your ex-husband maintain his Colombian citizenship? As far as I see from my research, a child born abroad to a Colombian mother or father can become a citizen once registered or domiciled in that country. Also, it only take the consent of one parent to obtain a Colombian passport for a child--though there are some travel restrictions.
Does your decree state who is in possession of her passport? Who has the right to make final decisions? It is usually the custodial parent (i.e. the one she "lives" with). Yes, he'll probably cause problems for you when you try to take her to Spain...but there is a big difference between taking your daughter overseas on vacation and taking her to visit a country where he may still have citizenship--assuming your aren't a citizen of Spain.
USA and Colombia have quite strong economic ties, but no telling what would be needed if something went wrong.
You really need to base this decision on YOUR experience with your ex-husband and the advice of a lawyer who can research international custody law.
Good luck. These decisions are never easy.
P.S. I just read your update. If you're not worried about him bringing her back, then it doesn't really matter WHERE he is taking her. It is just a question of how long she'll be gone. The decree usually provides the acceptable timeframes. Use that as a scapegoat...you don't have to allow additional time. Of course, there's not a lot you can do (except) file kidnapping charges if he says "Ok, we'll be back in a week"...and just stays longer. I'd still consult a lawyer and make sure he provides you with ALL flight and contact information.