I am gobsmacked by how rare this word is in our story! Etymonline.com says:

from PIE *bhle-was “light-colored, blue, blond, yellow,” from root *bhel- (1) “to shine, flash, burn,” also “shining white” and forming words for bright colors.

Definitely sky colors, and definitely slippery to modern English speakers — but I’ve seen the sky be salmon, gold, white, so very blue that it makes me weep. Now I’m fascinated to look at all the color words. After the poetry words.

• 1.007 He had a tall pointed blue hat,
• 1.017 and lasses going off into the Blue for mad adventures?
• 1.026 with a blue beard
• 1.038 both with blue hoods,
• 1.040 and they both swept off their blue hoods
• 1.092 Gandalf struck a blue light on the end of his magic staff,
• 3.013 and blue.
• 3.050 blue sky
• 4.002 where things were blue
• 4.035 into a tower of blue glowing smoke,
• 4.041 now it was bright as blue flame
• 5.035 in a blue face
• 6.064 Then he set one alight with bright blue fire,
• 6.064 one in blue flames,
• 7.116 green, blue, red, silver-grey, yellow, white;
• 8.106 by the tip of a blue hood sticking out at the top.
• 11.022 but of what lay beyond the blue distance,
• 15.044 and the blue banner of the Lake,
• 18.053 blue