Once I have the wrapper cased up to where I like it (like fine, plump, fluffy stretchy leather, no moistness) I let it dry a little bit by opening the mouth of the casing bag slightly; then I take it outside and mist it in direct sunlight, keep it in the sun for x minutes, then rebag it in a warmish environment; then repeat until I have the color I want. Then re-case as necessary to the right dry plump fluffy stretchiness. If the leaf is "good" then it doesn't lose stretchiness or burn quality with this procedure. This kind of moisture+warmth-to-darken technique goes back at least to 1850, which is about as far as I've found any documents on it. That's probably around the time that the marketers figured out that "brown = tasty" in the consumers' minds. That is the very reason people were patenting all kinds of "make it darker brown" techniques and devices in the 1800s and 1900s. I do it because I don't like greenish-beige.