We present the development of an innovative technology for quantitative multiplexed cytology analysis based on the application of spectrally distinctive plasmonic nanoparticles (NPs) as optical probes and on cost-effective side-illumination multispectral darkfield microscopy (SIM) as the differential NP imaging method. SIM is based on lateral illumination by arrays of discrete color RGB light emitting diodes (LEDs) of spectrally adjusted plasmonic NPs and consecutive detection by the conventional CMOS color camera. We demonstrate the enhanced contrast and higher resolution of our method for individual NP detection in the liquid medium and of NP markers attached on the cell membrane in a cytology preparation by comparing it to the conventional darkfield microscopy (DFM). The proposed illumination and detection system is compatible with current clinical microscopy equipment used by pathologists and can greatly simplify the adaptation of plasmonic NPs as novel reliable and stable biological multiplexed chromatic markers for biodetection and diagnosis.