첫사랑을 떠올리면 연상되는 색깔이나 노래
첫사랑 first love 연상 association 색깔 color 노래 song
떠오르다 means "to float". 떠올리다 is a causative form of "떠오르다", means "떠오르게 하다".
In English, you would say just "if you think of your first love" to mean "첫사랑을 떠올리면".
In 연상되다, -되다 is added to mean "to become/happen/come to...". 생각되다, 걱정되다 are other examples.
I'd translate the whole phrase like this: The color or song that you are associated with when you think of your first love