So I am taking an introductory particle physics class, and we have started learning about the leptons and how some particles, like neutrinos, have antiparticle pair based on a different in a different quantum number, like Lepton number. Another example is Neutrion and Anti-Neutron which differ in quark/anti-quark content. However, this got me wondering.... Do antiparticle/particle pair that are electrically neutral still annihilate with each other? What about quarks and anti-quarks of the same flavor? If so, is the interaction any different from Positron/Electron annihilation? Why don't quark/antiquarks of different flavors but equal and opposite charge annihilate?