Abstract: Disclosed are systems and methods for labelling one or more morphological markers in a biological sample that are characteristic of one or more molecular features. In particular, system and methods are described for labelling one or more morphological markers in a biological sample with covalently deposited narrow band detectable moieties. Narrow band detectable moiety labelling of the one or more morphological markers permits higher order multiplexed assays due to conservation of available spectral bandwidth. Furthermore, as compared to conventional counterstaining methods, covalent deposition of one or more detectable moieties can provide flexibility and robustness with regard to the order in which biomarkers and morphological markers are labeled in a given staining protocol.