High-quality short-wavelength-emitting ZnxCd1-xSe nanocrystals with emission wavelengths tunable from 440 to 550 nm have been prepared through the incorporation of a Zn precursor into the newly formed CdSe nuclei together with the remaining Cd/Se precursors (or Cd precursor into the ZnSe nuclei with the remaining Zn/Se precursors). The photoluminescence properties for the obtained alloyed nanocrystals (emission efficiencies of 45-70%, fwhm = 24-32 nm) are comparable to or even better than those for the best-reported binary nanocrystals. Moreover, the alloyed nanocrystals can retain their high luminescence (emission efficiency of similar to30%) if dispersed in aqueous solution. The most striking feature of the alloyed nanocrystals is their unusual long-time stability in emission wavelength/color, spectral width, and emission efficiency at high temperature. This is attributed to their characteristic structure (increased covalency and hardened lattice) and the strong bonding capability of the coordinating surfactant trioctylphosphine oxide to dangling Zn bonds at the surface of the alloyed nanocrystals. Through the embryonic nuclei-induced alloying process, highly luminescent and stable nanocrystals with different desired emission wavelengths/colors can be achieved reproducibly by only changing the synthetic recipe through adding the predetermined amount of reaction precursors. It is expected that the reported effective synthetic strategy can be developed into a very practical approach to high-quality color-tunable nanocrystals with narrow spectral width and high stability.