Rainbows from tears

I came across an image in one of Mrs. Oliphant's poems today that greatly appealed to me. The poem is "The Shadow on the Way" published in Blackwood's Magazine in June 1853. Mrs. Oliphant would have been 25 years old when it was published. The poem indicates that she had already experienced sadness and grief, but at 25 she was able to say:

Yet sometimes clouds, a frowning line
Will steal across those kindly skies;
And now and then some tears of mine,
Under this fair and soft sunshine,
Make rainbows to mine eyes.