A chemical solution deposition route to synthesize silver-gold alloy colloids in thin films with diameters between 8-35 nm has been developed. Ag-Au alloy colloids were synthesized by the addition of silver ions to a polymer protected aqueous gold sol in presence of a seeding agent 'hydroxylamine hydrochloride,' followed by a heat-treatment under reducing atmosphere at temperatures ranging from 150-550degreesC. The resonance wavelength of Ag-Au alloy colloids exists between those of pure Ag (410 nm) and pure Au (525 nm) colloids, which can easily be controlled by selecting the molar ratio of Ag to Au. This allows the tunability of the absorption wavelength ( hence the color) by using Ag-Au alloy colloids in thin films. (C) 2003 Kluwer Academic Publishers.