Afterglow nanoparticles (AGNPs) possessing inherently long lifetime with tailorable emission colors and uniform size have long been sought due to their time‐gating‐free high‐contrast multiplexing imaging. Herein, via a straightforward template method, it is reported that such multicolor AGNPs can be accomplished. The resultant AGNPs exhibit a series of tunable afterglow emissions, including blue, yellow, green, and white. These multicolor AGNPs are found to be highly bright, enabling them to perform high‐contrast multichannel afterglow imaging in vitro and in vivo without the use of any complicated time‐gating algorithms or systems, which existing tools are unable to do.