rather than SU(3) (8)SU(2)(8)U(l). The chiral-color group SU(3)z^0SU(3)/? breaks down to its diagonal subgroup SU(3)c at a mass scale comparable to that of electroweak symmetry breaking. Chiral-color models demand the existence of a wide variety of new particles including exotic fermions and spinless mesons with color and charge. A specific prediction of any such model is the existence of the axigluon, a color octet of electrically neutral gauge bosons with mass not greater than several hundred gigaelectronvolts. In Ref. 1, we present five illustrative chiral-color models based upon different choices of the anomaly-free fermion representation. In this paper, we focus upon what we now regard as the most promising realization of chiral color. We base our choice upon the following constraints that are reasonable to impose upon an alternative to the standard model which is to recapture the latter's past triumphs: I. The light fermions form a real representation of the exact QCD-QED group SU(3)c<S)U(l )^ . This is obligatory for any sensible theory. II. There are no triangle anomalies among the currents coupled to the gauge bosons of R. This yields two constraints upon the fermion representation, above and beyond those of the standard model, which must be satisfied if the theory is to be renormalizable. III. The electric charges of all fundamental fields are such that all color-neutral configurations have integer charge. There must be no isolable fractionally charged particles. IV. No fundamental field surviving at low energy carries electric charge greater than 1. This technical assumption excludes certain bizarre and unpalatable possibilities. Axioms III and IV imply that all quarks [i.e., fermons transforming as 3's of SU(3)c] carry electric charges j or — y . [A variation of Mark II (Ref. 1) requiring a quark of charge — 4 y is thereby excluded.] V. The left-handed quarks comprise TV weak doublets, while the right-handed quarks are all weak singlets. This ensures that the couplings of Z^ are flavor diagonal whatever the form of the quark mass matrix. This axiom is violated by Mark II of Ref. 1. In that model, the Glashow-Iliopoulos-Maiani (GIM) mechanism is undone by Z ^ couplings. VI. All left-handed quarks are triplets under SU(3)/, and singlets under SU(3)/?. Conversely, all right-handed quarks are triplets under SU(3)/? and singlets under SU(3)^. This is the gist of any naive implementation of chiral color and ensures that axigluon couplings are parity conserving and purely axial vector. More importantly, axiom VI guarantees that they are flavor diagonal. Marks I, III, and IV of Ref. 1 violate this axiom. For these models, potentially serious violations of the GIM cancellation of flavor-changing neutral currents can be induced by axigluon exchange. Axioms V and VI together ensure that the Glashow-Weinberg criterion^ may be satisfied for the Higgs-boson couplings: that no more than one Higgs boson need be introduced to give quarks of a given charge their masses, thus ensuring the absence of GIM-violating effects mediated by Higgs bosons. Except for Mark V, all of the models proposed in Ref. 1 violate one or another of the preceding axioms and present the threat of sizable GIM violation. These effects can be controlled by judicious choice of the fermion mass matrix with generalized mixing angles no smaller than those already observed in nature. We cannot logically exclude models which violate our axioms. Nonetheless, it would seem preferable to search for a theory in which the GIM mechanism is exact and automatic rather than approximate and imposed. VII. Our final axiom is the requirement that the chiral-color theory, like its predecessor, should be embeddable within a unified theory involving a single gauge coupling constant. The notion of grand unification is too attractive to be lightly abandoned. One and only one model described in Ref. 1 satisfies all of the above axioms. Furthermore, we are unable to identify any acceptable model distinct from Mark V. Under (SU(3)^ , SU(3)/?, U ( l ) ^ ) , the fermion representation which satisfies all seven axioms consists of the fol-