Breaking the restrictions of a lock-and-key sensing strategy which relies only on the most dominant interactions between the sensing element and target, here, we develop a colorimetric sensor array with three kinds of cationic polymers (polydiallyl dimethylammonium chloride (PDDA), chitosan (CTS), and cetyltrimethylammonium bromide (CTAB)) as nonspecific receptors. Diverse interactions between cationic polymers and proteins make gold nanoparticles (Au NPs) exhibit different aggregation behaviors, resulting in changes in color and absorbance of Au NPs. Based on the diverse colorimetric response patterns, seven proteins were successfully discriminated visually at the 20 nM level by linear discrimination analysis (LDA). Furthermore, the practicability of the sensor array was validated by the successful identification of proteins without any overlap in human serum samples.