Self-assembly of plasmonic colloids is a key challenge on the road to the cost-efficient fabrication of optically active surfaces. Here, we show that core–shell particles with plasmonic cores and hydrogel shells are ideal building blocks for coatings with engineered optical properties. The plasmonic properties of the colloids are tuned by selective overgrowth of the gold cores with either gold or silver shells of variable thicknesses. This library of particles is used for monolayer preparation by self-assembly at the air/water interface and subsequent transfer onto solid supports. These monolayers of hexagonally packed particles have very similar particle densities and center-to-center distances, independent of the metal core composition and size. Consequently, our simple and robust bottom-up approach allows us to precisely tailor the optical properties of solid surfaces.