Definition of "bluer"

Bluer buttons illustrate the principle of 'keeping under'. The Knoll rule book states: 'It is a one year priv. [privilege] to have the bottom button on one's bluer undone [and] a three summer priv. to have all the buttons of one's bluer undone.'

1981, James Anthony Mangan, Athleticism in the Victorian and Edwardian Public School, Psychology Press, published 2000, page 170

He was alone in his room, in his bluer and his tie, seated on a chair, leaning over his bed like a desk—his preferred way to study—holding the stapled pages of the script, muttering the words.

2011, Justin Evans, “Voraciously”, in The White Devil