While the aberrant low expression of metallothioneins (MTs) in tissue has been recognized as an effective indicator to spot the occurrence of early-stage malignant tumors, the ultra-sensitive detection of MTs at a low concentration (< 10 nM) remains to be developed. Here, a facile multicolor colorimetric visualization strategy is introduced to detect MTs at an extreme low concentration down to 28 pM, enabled by the catalytic activity-modulated etching of plasmonic gold nanorods (CAEPAu). The catalytic reduction is inhibited by covering the nanospheres with highly specific protein corona recognizing MTs, thus facilitating a customized etching of nanorods (NRs) into nanospheres to present color correspondingly. The CAEPAu assay detects MTs in 35 min, significantly faster than the existing method (~3 hours). We demonstrate to use CAEPAu assay to precisely detect and distinguish MTs in four tumor cells, clinic blood samples and other proteins.