I have yet to try damiana, as this is the first time I'm hearing about it. But absinthe I'm quite familiar with. In Berlin I used to drink one called "Versinthe", which despite it's name was completely clear until mixed with water. Then it would become cloudy milky colored. I enjoyed the feeling of creativity and euphoria it caused. Unlike alcohol I didn't lose my coordination, but it got me moving... being able to walk and talk through the whole night.
At the absinthe shop I used to buy it, the vendor explained to me that the green color came from the days when it was still legal in France, but not in Spain. So they smuggled it into the country in bottles of hair-tonic, with a green die added to make it fit the label. Though I don't know if this goes for absinthe in general, or just this Versinthe.