I’m writing about indigo right now, about that blue that is sort of the outlier in the colour spectrum, a between colour (and I have my own theory about why but will let this wait until I’ve finished the essay). In the meantime, I am looking at blue, at the dictionary definitions (using my Shorter Oxford English Dictionary on Historical Principles, sixth edition), at fabrics dyed on the cedar log near my vegetable garden on summer mornings while pileated woodpeckers taught their young to feed nearby, at beautiful examples of Japanese textiles, at the hands of Tuareg people who wear indigo-dyed clothing and have stained skins as a result, and more. I am living in blue (“taken as the colour of constancy, taken as the colour of sorrow and anguish”).
...Theresa Kishkan 
In certain latitudes there comes a span of time approaching and following the summer solstice, some weeks in all, when the twilights turn long and blue. You pass a window, you walk to Central Park, you find yourself swimming in the color blue: the actual light is blue, and over the course of an hour or so this blue deepens and approximates the blue of the glass on a clear day at Chartres, or that of the Cerenkov radiation thrown off by the fuel rods in the pools of nuclear reactors. The French called this time of day “l’heure bleue”. To the English it was “the gloaming.” The very word “gloaming” reverberates, echoes – the gloaming, the glimmer, the glitter, the glisten, the glamour – carrying in its consonants the images of houses shuttering, gardens darkening, grass-lined rivers slipping through the shadows.
During the blue nights you think the end of day will never come. As the blue nights draw to a close (and they will, and they do) you experience an actual chill. The blue light is going, the days are shortening, the summer is gone.
Joan Didion’s Blue Nights
Oh isn’t that beautiful.