Is CP-Invariance Violation Caused by an SU(3) Singlet?

A theorem is proved which shows that if $\mathrm{CP}$-invariance violation originates in a semistrong and/or electromagnetic—or in fact any—interaction belonging to a $(3^{*},3)\oplus (3,3^{*})$ representation of $\mathrm{SU}\mathrm{}\left(3\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(3\right)\mathrm{}$, the $\mathrm{CP}$-invariance—violating term is a pure singlet of SU(3).