Herein,　we　report　for　the　first　time　a　colorful　chromogenic　substrate,　which　displays　vivid　color　responses　in　the　presence　of　different　concentration　of　analytes.　Our　investigation　reveals　that　the　selective　shortening　of　gold　nanorods　(AuNRs)　could　generate　a　series　of　distinct　colors　that　covers　nearly　the　whole　visible　range　from　400　to　760　nm.　These　vivid　colors　can　be　easily　distinguished　by　the　naked　eye;　as　a　result,　the　accuracy　of　visual　inspection　could　be　greatly　improved.　Next,　we　demonstrate　the　utility　of　AuNRs　as　multicolor　chromogenic　substrate　to　develop　a　number　of　colorimetric　immunoassay　methods,　e.g.,　multicolor　enzyme-linked　immunosorbent　assay　(ELISA),　multicolor　competitive　ELISA,　and　multicolor　magnetic　immunoassay　(MIA).　These　methods　allow　us　to　visually　quantify　the　concentration　of　a　broad　range　of　target　molecules　with　the　naked　eye,　and　the　obtained　results　are　highly　consistent　with　those　state-of-the-art　techniques　that　are　tested　by　the　sophisticated　apparatus.　These　multicolor　portable　and　cost-effective　immunoassay　approaches　could　be　potentially　useful　for　a　number　of　applications,　for　example,　in-home　personal　healthcare,　on-site　environmental　monitoring,　and　food　inspection　in　the　field.