Localized surface plasmon resonances (LSPRs) have a broad technology potential as an attractive platform for surface-enhanced spectroscopies, refractive index sensing, hyperthermal cancer therapy, plasmon-enhanced catalysis, and so on. One of the newest metals for plasmonics is magnesium. It is earth-abundant, biocompatible, and has a higher plasmonic quality factor than aluminum across the visible (and than gold and copper in the blue). In the past ten years, several fabricated magnesium structures have emerged, demonstrating the optical behaviors expected of plasmonic metals. Our group has chosen a different approach: we have developed colloidal, scalable batch and flow syntheses capable of size control from ~50 to 1000 nm. This talk will review the advances we have made over the past six years on colloidal magnesium plasmonics, with a focus on the fascinating size and shape-dependent optical, chemical, crystallographic and catalytic properties of these novel structures.