Current　methods　for　tuning　the　plasmonic　properties　of　metallic　nanoparticles　typically　rely　on　alternating　the　morphology　(i.e.,　size　and/or　shape)　of　nanoparticles.　The　variation　of　morphology　of　plasmonic　nanoparticles　oftentimes　impairs　their　performance　in　certain　applications.　In　this　study,　we　report　an　effective　approach　based　on　the　control　of　internal　structure　to　engineer　morphology-invariant　nanoparticles　with　tunable　plasmonic　properties.　Specifically,　these　nanoparticles　were　prepared　through　selective　growth　of　Ag　on　the　inner　surfaces　of　preformed　Ag-Au　alloyed　nanocages　as　the　seeds　to　form　Ag@(Ag-Au)　shell@shell　nanocages.　Plasmonic　properties　of　the　Ag@(Ag-Au)　nanocages　can　be　conveniently　and　effectively　tuned　by　varying　the　amount　of　Ag　deposited　on　the　inner　surfaces,　during　which　the　overall　morphology　of　the　nanocages　remains　unchanged.　To　demonstrate　the　potential　applications　of　the　Ag@(Ag-Au)　nanocages,　they　were　applied　to　colorimetric　sensing　of　human　carcinoembryonic　antigen　(CEA)　that　achieved　low　detection　limits.　This　work　provides　a　meaningful　concept　to　design　and　craft　plasmonic　nanoparticles.