"Tomorrow is Tuesday, right?"
Translation:Morgen ist Dienstag, richtig?
'Morgen' can mean either 'morning' or 'tomorrow'. Both are capitalized since they are both nouns. And just as in English, the first word in German always starts with a capitalized letter. In your sentence "Dienstag ist Morgen, richtig?", it seems it would make sense but I would say that "Morgen ist Dienstag, richtig?" is more natural.