Analysis of Fragmentary Blue

Why make so much of fragmentary blue
In here and there a bird, or butterfly,
Or flower, or wearing-stone, or open eye,
When heaven presents in sheets the solid hue?

Since earth is earth, perhaps, not heaven (as yet)--
Though some savants make earth include the sky;
And blue so far above us comes so high,
It only gives our wish for blue a whet.