"주황색 바나나는 맛없어요."
Translation:The orange banana tastes bad.
Um ~는 is a topic marking particle along with ~은. I think it basically just tells people what you are going to talk about. For example: The commonly used word "저" needs the particle ~는 added to it.
저 = I 저+는 = As for me, me 저는 학생이에요. = As for me, i am a student
To Korean people, it wouldn't make as much sense to them without the ~는 following 저.
Basically, you add ~는 after 저 because 저 is the topic of the sentence (as well as the subject).
내일은 저는 일해요. = As for tomorrow, i work.
Here, 내일 (tomorrow) is followed by ~은 because it is the topic of the sentence, however, it is not the subject of the verb 일하다, because it is not 'tomorrow' that works, but 'I' that works.
-if you need more help use TTMIK, Level 1, Lesson 9- Yes i did basically just copy out of my grammar notes from that section. All the credit is to the TTMIK team :)