Were he to see the light of his face in hers would mean that she is in the light, that there is a connection between the two of them, a yearning for him as a submissive bride, which there is no longer. Here she begins to equate flowers with the upper-world, Orpheus world, LIFE, for which she has longed. In place of this existence, Eurydice yearns for earthly beauty. For her, flowers symbolize the epitome of earthly existence. She is stuck here, though.
Crocuses are also among the very first flowers of springtime.
So we have sky, sun wind, all of which are beyond her intrinsic grasp now. The stigma and style are components of the flower's reproductive mechanism. That Eurydice should compare Orpheus to saffron suggests that he is, like commercially produced saffron, pulverized and used thus. Notice this line in his letter as nothing less than an affirmation of H.D.'s closing to the poem. I do not know whether H.D. knew of this letter to Gray going into her poem, but the parallel in thought is indeed startling.