Electric Charge of Quarks
The proton has a quark composition of uud, and so its charge quantum number is:
q(uud) = 2/3 + 2/3 + (-1/3) = +1
The neutron has a quark composition of udd, and its charge quantum number is therefore:
q(udd) = 2/3 + (-1/3) + (-1/3) = 0
Since the neutron has no net electric charge, it is not affected by electric forces, but the neutron does have a slight distribution of electric charge within it. This is caused by by its internal quark structure. This results in non-zero magnetic moment (dipole moment) of the neutron. Therefore the neutron interacts also via electromagnetic interaction, but much weaker than the proton.