In contrast to a macroscopic solid, the color and spectroscopic properties of gold nanoparticles change with size. Here, we propose a teaching platform for high school students (hereafter defined as students, attending secondary school in Europe, preparatory high schools in the US, or any educational institution of a comparable level) that explains the relationship between the perceived color of colloidal solutions and their physicochemical properties. For this aim, an open-source code, based on Mie theory and colorimetry, was developed to link the perceived colors to the plasmonic effects. Moreover, a set of such nanoparticles, varied in diameter, was created to support the theoretical description. The employed seed-mediated synthesis approach provides sufficient spherical roundness that is crucial for color matching. The proposed teaching platform is available online and can be linked to an outreach activity or practical laboratory course. Furthermore, we illustrate the linkage of nanoscience concepts to real-world examples (e.g., stained church glass), which can be used for promoting the potential of nanotechnology in other fields, including electronics, optics, and biomedicine adding to the interdisciplinarity of the teaching platform.