Cerulean

Noun

 * 1) A deep blue colour, like the sky on a fine day.
 * 2) sky blue

Adjective

 * 1) Of a deep blue colour, like the sky on a fine day.

Thesaurus
Caelus, air, azure, azure-blue, azure-colored, azurean, azured, azureous, beryl-blue, berylline, blue, blue sky, bluish, caelum, canopy, canopy of heaven, ceruleous, cerulescent, cope, cyanean, dark-blue, deep-blue, empyrean, ether, firmament, heaven, heavens, hyaline, lift, lifts, light-blue, lightish-blue, livid, pavonian, pavonine, peacock-blue, sapphire, sapphirine, sky, sky-blue, sky-colored, sky-dyed, starry heaven, the blue, the blue serene, turquoise, vault, vault of heaven, welkin

Etymology
From caeruleus: