The key is on the left... yellow is tracker hits (charged particles only), red electromagnetic calorimeter deposits (could be anything, but electrons and photons leave larger deposits as they should stop), blue is hadronic calorimeter depoits (anything not stopped in the electromagnetic calorimeter, so probably not electrons of photons). Muons will show up in all these detectors are reach the other muon systems.

The beam isn't shown, but the estimated primary vertex is (where the two protons collided).