The combination of different metals into a discrete colloidal nanocrystal (NC) lattice to form solid solutions can result in synergetic and non-additive effects, leading to physicochemical properties distinct from those observed in monometallic NCs. However, these features are influenced by parameters that are challenging to control simultaneously using conventional synthesis methods, including composition, morphology, size, and elemental distribution. In this study, we present a methodology that exploits seed-mediated growth routes and pulsed laser-induced ultrafast heating to synthesize bimetallic and trimetallic colloidal alloy NCs with tailored compositions, well-defined spherical morphologies, and precise control over the number of atoms per NC lattice. Initially, core-shell heterostructures with adjustable compositions and