Bluish means slightly blue in colour. A bluish tinge, bluish grey, bluish in the light.
The -ish ending hedges, which is exactly what colour words need — very little in the world is a pure colour. Bluish lips or fingers are a clinical sign of low oxygen and a reason to seek help. Note the spelling, which drops the e of blue, and blueish, which is also accepted.
1adjectivebluishSlightly blue in colour.
“The mountains looked bluish in the distance.”
bluish is a colour quality.
Middle English blewissh is blue plus -ish, an ending meaning somewhat. Greenish and reddish are formed the same way.
Middle English
blewissh
English, today
bluish
From Middle English blewissh, blewisch (also Middle English bloysh), equivalent to blue + -ish.
Etymology from Wiktionary, CC BY-SA