particle physics - Electron/Proton Charge and Quarks Charge

So.. I´ve been investigating a bit on the subject of sub atomic particle charges and how they were defined, and basically what I´ve found out is that the defenition of the charge of an Electron or a Proton is totally arbitrary.

But then I remembered about the up quarks and down quarks and I got a bit confused because we say that a proton is positive due to the fact that it has 2 up quarks and 1 down quark, and that the up quark has a positive charge and the down quark has a negative charge.

My question is, is the charge of the up quark and down quark also arbitrary ?