yellow ones are on every route, green ones are only on neutral, blue ones are only on pacifist, and red ones are only on genocide, and orange are just places also, if it has a purple border, its a final boss of that certain route finding an interactive undertale album, it fills you with... detemmienation
credit to RicchardEB for making the album this contains major spoilers to all 3 routes there are some not on here, reason: RicchardEB hasn't remixed them yet, for example, the amalgams, or glad dummy, or song that might play when you fight sans
