In the US, blue can mean something improper, such as a comedian "working blue" meaning adult language and humor. Is it also used in this context in Norwegian? Or can it only literally mean a blue colored book?
I felt sure in the previous "lesson explanation" that an example was given
"ei blå bok" ..whilst in this lesson it is "en blå bok".
If certain nouns can have alternative genders then perhaps this could be explained.