"Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within baryons or mesons.
This sentence makes me very nervous: Due to a phenomenon known as color confinement
This sentence is Like I want to prove something spurious to save the subject (quark)."
Coodan answer:
"OK, I think, you are completely right with your lawful doubts.
We had seen that kind of approach in Medieval Years. That time they told us that it is possible/impossible to count the number of angels on the top of the needle. Angel/demon confinement? :))))
The truth is that Chadwick in 1932-1934, knowing no negative particles except from electron told them that neutron is elementary particle like proton with no real proof. Just (speculative!) statement. Sakawa, then Gell-Mann trusted that very and as a result we have quark model with fractional charges.
In fact, apart from that strange beliefs about neutron, we have to confess that neutron is composite particle consisting of proton and negative pion, so idea of fractional charges of quarks is just an error.
No fractional charges is possible in the Nature. Limited is our understanding."