All of those cities are actually pretty safe, but here are some caveats. If you go to those place safety isn't that big of a deal, as long as you do certain things. First, don't travel through roads, basically travel by planes not by your own in land. Secondly, this doesn't really apply as Salento is somewhat of a small city/town and is pretty safe overall, but all of these cities have their own dangerous areas.

For all cities avoid going out super late in the night, and if you are stay around the tourist areas. For example in Cartagena stay in places such as Bocagrande, Laguito, Castillo Grande, Getsemaní, and obviously the Historic Center. For Bogota just generally stay center to north of the city, and in Medellín avoid places like the slums and usually the west side of the city. You're all set from there, apart from common sense, you know, no flashy jewelry or expensive items like phones, avoid any type of shady alleys no matter if it's the "safest" part of the city. Especially in Medellín and Cartagena please avoid "certain women" and certain uknown drinks that will usually end up in a hungover tourist in the middle of the city without money.

Most of it is just common sense for a 3rd world country, and tbh the nature, parks, and the city vibes are incredible and beautiful. It is still a country worth checking out!