Ag@zinc–tetraphenylporphyrin (Ag@ZnTPP) core–shell nanostructures have been fabricated by in situ chemical deposition. Unusual thickness-dependent fluorescence allowed their colour to be tuned from blue to red by simply increasing the shell thickness from ∼2 nm to ∼9 nm. The competition between metal enhancement and the self-absorption effect of ZnTPP has been shown to be the main reason for this variation.