Definition of "hadron"

The weak decays of b hadrons are dominated by the spectator model process whereby the b quark decays to a c quark (or occasionally a u quark) with the emission of an external W, while the non-b antiquark or diquark acts simply as a passive spectator to the decay.

1996, J. R. Batley, “Measurements of B Hadron Lifetimes at LEP”, in Michael C. Birse, G. D. Lafferty, J. A. McGovern, editors, Hadron '95: The 6th International Conference on Hadron Spectroscopy, World Scientific, page 48

One can use the lattice simulations, which do represent the rigorous consequences of non-perturbative QCD, as guidance for models of hadron structure.

2005, D. B. Leinweber, A. W. Thomas, R. D. Young, “Hadron Structure and QCD: Effective Field Theory for Lattice Simulations”, in Alex C. Kalloniatis, Derek B. Leinweber, Anthony G. Williams, editors, Lattice Hadron Physics, Springer,, page 114

And hence colour, which was initially an ad hoc concept, later turned out to be an empirically confirmed reality of hadrons.

2017, Syed Afsar Abbas, Group Theory in Particle, Nuclear, and Hadron Physics‎, Taylor & Francis (CRC Press / Chapman & Hall), page 204