Now I know you are full of shit. In late flower you want to see some nitrogen deficiency IMO. Just a little and only late. That means the plant isn't getting too much nitrogen which makes for dark green bud that burns harsh.
ah man
its a good thing that you speak about that
during years i made my plants yellow at the end to have that nice autumn fade. i was sure that chlorophylle ( nitrogen, the green of leaves) was a bad thing
i was wrong i recently discovered that the best buds always comes from the less yellow plants
because the green in your leaves, when you hang your plant in the dark after harvest, will continue to work and plant will tranform it into sugar
i may be wrong in the precision of the processus, but its a fact
color of the ash has nothing to do with color of the plant
in fact you will even notice that the greener plants will produce the thinest and whitest ashes
because the chemistry would be respected
the culprit for dark shinny ashes are p and k, found in bloom nutrients or boosters
if there is some remaining in the medium at harvest, you will have it in your weed
nobody can feed perfectly especially in soil with organics, so its necessary to let the plant consume the remaining phosphorous and potassium before chop ..