Learn Swedish: Jag hoppas att det nya badrummet är blått. - I hope that the new bathroom is blue.

Blå is describing badrummet, which is a neuter (ett) word. Normally, you add -t to an adjective for ett words. However, because the base form blå ends in a stressed vowel, you must add -tt. This spelling change also shows that the vowel sound becomes short.

If badrum is an ett word, why isn't the word for 'new' also in the neuter form (nytt)?

Because it is part of a definite phrase (det nya badrummet). When an adjective comes directly before a definite noun, it takes the definite ending -a, regardless of the noun's gender. Blått, on the other hand, comes after the verb (as a predicative adjective), so it keeps the standard neuter ending to match the noun.

Why does the sentence say det nya badrummet instead of just det nya badrum?

Swedish uses a 'double definite' system. When you put an adjective (nya) in front of a definite noun, you must use both the separate definite article (det) and the definite suffix on the noun itself (-et in badrummet).

If I wanted to say 'I hope the new bathroom is NOT blue', where would inte go?