Dragon flight (for Marianne )

[RiverNotch]

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Fiery breath lights blackest night,
a ruby comet falling fast, Probably best to use a semicolon instead of a comma here. And metrically, it feels somewhat off.
beating wings of dragon’s flight,
know this sight to be your last. I think an exclamation point would make this more forceful, making the metamorphosis more harsh and exciting from the onset.

Like the clouds up in the sky,
part will live, part will die, Even though the speaker doesn't mean to make a definite division between who will live and who will die, using more definite terms (like half) instead of the word part will make it sound more forceful, which again will highlight the dragon's change. And add an "and" between the two halves of the line, to fix the meter.
the lowest lows, the highest highs, This muddles up the message of the line before it. Best to change the idea in this line to something more supportive.
as the dragon shows its might.

Burning red a pulsing disc,
follows orange, and then the green, I suggest removing the "and" and replacing "the green" with "a green". Oh, and I think a semicolon would be a nice ending here.
rising force a willow wisp,"rising force, a willow wisp" just sounds better, and to me, somewhat adds a bit of sense to a line I don't exactly understand.
up the spine, remains unseen.

Now the blue and the violet, Remove the "the" in "the violet" to make it speak smoother. Also, the comma shouldn't be there.
opens up the unseen view,
overwhelmed by sinking silence, I think the meter isn't clean here.
bewildered mumblings, oft confused.Again, the meter's somewhat off. And the oft confused part just seems redundant: if it's the "bewildered mumblings" that're "oft confused", then... well, bewildered mumblings are generally confused (confused being a synonym to bewildered), so it's, well, redundant.

When at last the storm is over, Meter's still off. Or maybe I've just been following a different sense of rhythm throughout most of my reading... No, I don't think so. "When, at last, the storm is done" fits the whole poem better. Oh yes, and the "at last" should be separated from the rest of the line with commas. But the ending should be left open; that is, comma/semi-colon/period-less.
and the light comes from above, "the light" doesn't feel right... I think a short descriptor to this light should be what modifies it, something that adds to the light's sense of relief to the turmoil.
note with awe the transformation,Meter feels off again. And I think a colon should end this line.
dragon’s now become a dove.The wording doesn't feel right again, but now I don't really know what's off about it: possibly a dearth of poeticality (damn, that is an awful word)? Also, an exclamation point I think should again end this, just to make the whole change feel more awe-inspiring.

©2014 –Erthona

nota bene: accentual verse in tetrameter I'm betting my suggestions on meter were born of me not noting this... Ah, well, for those suggestions I wrote what I felt. Best to take heed of them, but with heaping spoonfuls of salt.

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The whole theme of the poem, the change of the dragon into a dove and the violence this metamorphosis exudes, it's absolutely brilliant! And I'm betting if one got all of the references to the colors and such the poem would be seem even more brilliant. Most of the problems I highlighted up there have already been highlighted, but they're mostly little problems, problems on execution: in other words, your poem is, as the transformation it detailed, awful.