Technology

For anyone who is also not from the US:

A blue book exam is a type of test administered at many post-secondary schools in the United States. Blue book exams typically include one or more essays or short-answer questions. Sometimes the instructor will provide students with a list of possible essay topics prior to the test itself and will then choose one or let the student choose from two or more topics that appear on the test.

EDIT, as an extra to solve the mystery:

Butler University in Indianapolis was the first to introduce exam blue books, which first appeared in the late 1920s.[1] They were given a blue color because Butler's school colors are blue and white; therefore they were named "blue books".