Blue

While the Japanese title is linked to ブルー, the info taken is from 青.

Blue (青/あを ao \ ブルー, burū) is one of the basic colors. It refers to a color similar to the sky during a well-sunlit day, the sea, or lapis lazuli.

In English-speaking countries, it was considered a sexual color when pornographic films were called blue films. Now just like other countries, the most popular usage for a sexual color is red and pink.

In pixiv, it is used as a color tone tag.

As a concept, it includes a wide range of colors, and is also a generic term for blue-toned colors such as indigo, pale blue, deep blue, dark blue, ultramarine, ect.

In Japan, blue, dark blue, green, and other colors were once collectively called ao (青/あお).

Because of this, there are still many names for green things that are called ao (e.g., caterpillar (青虫), green leaf (青葉), green signal (青信号), green apple (青りんご), etc.). The kanji for ao (蒼) also reads ao (あお) but actually refers to a greenish color.

The katakana burū (ブルー) is borrowed from English's blue.

As a symbol, blue is associated with the four elements of water, and its coolness makes it the color of calmness and intelligence. It is often paired with red, the color of fire, as in "blue for intelligence, red for passion".

Blue is one of the three primary colors of light, along with red and green. The three three primary colors of color used in printing are magenta, yellow, and cyan, where cyan is translated as blue.

Indigo　Pale Blue　Deep Blue

青 / ブルー