Hi Lichen Lovers,
Just wanted to mention to all those who like edible forest gardens, that many lichens are edible also.
The only thing to watch out for is to avoid all yellow, or yellowy (orange) species,
as they may contain poisonous levels of vulpinic acid or usnic acid (both of which are yellow).
for rocks are rock tripe (which is black), Parmotrema perlatum )whic
for ground iceland moss
and reindeer moss (which is white) though note if it gets much sun exposure it accumulated usnic acid.
for trees Wila (brown versions) mostly in humid mountains,
also likely any white/green/black lichens should be fine also.
generally since they are so slow growing they are a delicacy,
but still if you manage to grow a large amount it can become a regular spice.
For most of them it seems best to cook in order to make it easier to absorb,
so as a spice to add to raw ingredients of soups, stir fries and other cooked dishes.
Another thing to note is that the environment affects all plants/lichen,
so even if it is a suitable color but growing in a toxic environment,
or on a poisonous tree (yew) then it would be best to avoid it.
Lichen is also a good pollution indicator:
Lecanora conizaeoides typically looks like green pots filled with yellow,
it can grow in very high pollution environments. I'd avoid eating them.
Lepraria incana looks overall pale green and fuzzy,
it can grow with high pollution.
Hypogymnia physodes and/or Parmelia saxatilis or P. sulcata are pale green with branching "leaves",
these can grow in moderate pollution, and would probably be the first level safe to eat.
Usnea ceratina a green hair like lichen appears in fairly low pollution environments,
these hair-like ones are likely as good as Wila to eat, and increase the growing area by extending outwards,
so if you can, certainly do grow them.
As a final note, I think there can be a time and a place for yellow lichen,
such as places which you don't want animals to eat, or don't want yourself to accidentally consume.
One idea for it is around the trunks of young saplings, as an alternative to other winter protection schemes.
Another would be to grow in known toxic areas, such as where there were chemical spills.
it is similar to the yellow of caution tape, but longer term and self-renewing.
 Lichens for food https://en.wikipedia.org/wiki/Ethnolichenology#Lichens_for_food
 Lichens for air quality http://www.air-quality.org.uk/19.php