Hello! Welcome to the wonderful world of colombians!! They are absolutely my favorite of the tegus!
I've been working with two vets with my little guy, so I've got some backing to what I say as well as a few years of practical experience. I work as a research assistant in a medical education facility, so I've got access to pretty every journal out there. There are only a few papers that have anything to do with colombians, and the few that do are not trying to find things out about colombians specifically. Their research is to extrapolate information and use it broadly in terms of lizards. Basically, not very helpful.
First thing I'll tell you, there is hope!! My Blake is a total sweetheart. He's been dressed up for Halloween and entered in contests. He was in my wedding. I've taken him just about everywhere with me and have had no problems letting people handle him. He's a total sweety. However, it didn't come easy. I got him when he was a little less than two months old and he was nasty. Time, patience, and consistency are the key. Be consistent and you shouldn't have many problems.
As far as diet goes, colombians are almost exclusively meat eaters. Fruits and vegetables make up a very small portion of their natural diet. There are other tegus who eat a lot more fruits and veggies, but colombians are NOT one of them. I'll give you my feeding schedule for Blake.
Sun. - Canned monitor diet
Mon. - 4 fuzzies (he's been refusing mice of late)
Tue. - Canned monitor diet
Wed. - 4 fuzzies
Thur. - Canned monitor diet
Fri. - Tegu smoothy (various fruits and veggies, eggs w/shells, bone meal, and MinerAll I)
Sat. - Canned monitor diet w/MinerAll I
As you can see, he only gets fruits and veggies once a week and that's about all that he will stand for. Blake is also an adult so he doesn't need to be supplemented as often. I know that this food regimen works because I've had blood work and an x-ray done on him and everything has checked out perfect. As far as a juvenile goes, I would probably be supplementing three times a week and definitely feeding mostly protein foods.
Good luck! And if you have any more questions, I'm more than happy to help you out with whatever I can!
Lindsay