When you hop on that trolley, make sure your colors correct
When you take the bus or really go anywhere, make sure the colors you’re wearing are the right ones, or the gangs will take offense and kill you.
He is also alluding to the last line. Coroners use trolleys to move corpses. If you hop on that trolley, you’re a corpse.
Furthermore, (apparently). There’s a trolley system that runs through Compton and Lynwood and depending where you are hopping on you might encounter a blood or crip. Hence the next line.
To help improve the meaning of these lyrics, visit “M.A.A.d City” by Kendrick Lamar (Ft. MC Eiht) Lyrics and leave a comment on the lyrics box