[en] Three problems in hypothetical unified theories of electromagnetic, weak, and strong interactions are discussed here. First, the problem of embedding color in any simple gauge group is solved, and a complete classification of theories where the fermion color is restricted to 1/sup c/, 3/sup c/, and 3/sup c/ of SU/sup c/₃ is given. Generalizations are also indicated. Second, an unbroken U₁ generated by electric charge is embedded into each of the above theories and the charge assignments analyzed. Third, the general problem of stabilizing the proton by a suitable atomic mass number A is studied for the same set of theories. It is always possible to define A if the gauge group is not too small. In many of these theories there must be fermions with weird values of A: leptons with Anot =0 and quarks with Anot =1/3. Examples are discussed. Some future directions of research are indicated