When I get tacos from a taco truck or the more authentic Mexican restaurants here, the soft corn taco shells often have a somewhat oily texture and are a darker color than the shells are prior to being warmed/cooked. Here is one example and here is another example
How do they get the texture to be like that? I've tried using some oil when I warm the tacos in a pan, but that starts to make them crispy (the shells that I'm trying to replicate don't have burnt crispy spots) and the color doesn't get darker like trucks and restaurants manage. It also seems like the good chefs get the taco shells to have a more complex taste, whereas when I've tried it with oil or with no liquid, the shells aren't as tasty.