Miles develops the present image in Our Southern Birds:

This is the bluest of things blue, I do believe, in all the country,--like a drop precipitated by the delicate azure that is held in solution by the summer air. Blue we see in the velvety skies of the region; it hangs like a veil of flame--the thin violet flame of certain gases--over the sides of mountains and is reflected in the river; it is accented by bluebells, blue phlox, tradescantia and bluets; in this bird it flashes fire!--a color deep as a turquoise, burnished like a sapphire, dusky on the wing feathers and darkening to indigo only on the head. (127)