adjective

of a colour intermediate between green and violet, as of the sky or sea on a sunny day.

the clear blue sky

sky blue,azure,cobalt (blue),sapphire,cerulean,navy (blue),saxe (blue),Oxford blue,Cambridge blue,ultramarine,lapis lazuli,indigo,aquamarine,turquoise,teal (blue),cyan,of the colour of the sky,of the colour of the sea