Hi Beau! Great Pic!!!
So the Colombian won't eat too much? What did the previous owner/dealer feed him before coming under your care? That could be a good place to start. Since your blue is eating fine, your cage temps must be okay then.......
Another factor could be any size differences between your blue and the B&W. Does their size differentiate substantially? This commonly happens to smaller ones housed with larger tegus. The feel intimidated, will hide most often, thus hindering their appetite as well.
If the above are non-factors, you may want to try chicken. We boil it until almost fully cooked. Doesn't matter if it is wings, legs, etc. Sprinkle with Vit D3 and calcium supplemnt first. This hopefully will trigger his appetite. I have also found that is a tegu was previously fed live prey, such as pinkies, it will take them a while to acclimate to non-live prey.
We will feed our Arg & Paraguayans the SDZ as their main staple, then change up with chicken, eggs (very little). Colombians may not like the SDZ too well because of the fruit content, though each one is different. Even our new little gold devoured his SDZ, so this will be a test with each tegu, primairly the colombians.
You may want to attmept to soak him as well, if you have/do not already. I have found that tegu appetites can also deter if they are slightly dehydrate. They should always though be supplied with a shallow water bowl.:0) The last factor would be to get his fecal tested for potential parasites, if not done already.
My best wishes!!!
Greg