English for Today by Ganiu Abisoye Bamgbose (Dr GAB)
SINGULAR NOUNS IN IDIOMS
One of them wrote to us out of the ~blues~ several years later (nonstandard).
One of them wrote to us out of the blue several years later (standard). If something happens out of the blue, it happens unexpectedly.
You need not like my choice; beauty lies in the ~eyes~ of the beholder (nonstandard).
You need not like my choice; beauty is in the eye of the beholder (standard). This expression means that what one person finds beautiful or admirable may not appeal to another.
GAB