My nine year old son fought hard on this and is taking a stand on spelling bluish as blueish. I’m certain his teacher will mark it as a spelling error in his writing… Several dictionaries have indicated both spellings are acceptable. A character in his story says
What is that blueish white piece of
ice floating in the freezing cold
Both the NOAD and the OED define blueish simply as “spelling variant of bluish.” (See also bluish on the Oxford Living Dictionaries.)
Looking for both the words in the Corpus of Contemporary American English, there are 7 sentences containing blueish and 559 sentences containing bluish; for the British National Corpus, the numbers of the sentences are respectively 4 and 55.