This paper reports wide-range tuning of localized surface plasmon resonance (LSPR) wavelength using silver (Ag) and gold (Au) alloyed nanoislands for wafer-level fabrication of subtractive plasmonic color filter. The fabrication method includes concurrent thermal evaporation of Ag and Au sources to deposit thin alloy metal film onto quartz wafer, followed by thermal dewetting process to generate Ag-Au alloyed nanoislands. The LSPR wavelength of the alloyed nanoislands can precisely be controlled by adjusting the alloy deposition rate during the evaporation process. The subtractive color filters are fabricated by repeated lift-off processes of different Ag-Au alloy fractions, allowing facile wafer-level fabrication. The application of wide-range LSPR tuning of Ag-Au alloyed nanoislands is not only limited to subtractive plasmonic color filters, but also encompasses numerous possibilities for other engineering fields, such as, surface enhanced Raman spectroscopy and plasmonic enhanced fluorescence.