One-equation partition regularity over odd integers (${\sum }_i{a}_i=0$)

A rational homogeneous equation ${\sum }_i{a}_i{x}_i=0$ has a monochromatic positive odd solution in every finite colouring of the odd integers exactly when its full coefficient sum is zero. Sufficiency uses a constant odd vector. For necessity, clear denominators and, if the total $S$ is nonzero, colour by odd residue classes modulo $2^K>|S|$. A common odd residue is invertible, so a solution would require $2^K\mid S$, impossible. This is stronger than the zero-sum-subset criterion for unrestricted partition regularity.