A low content of chromium (<= 5 mol %) has been incorporated into a SnO2 cassiterite by a coprecipitation route in a basic medium, followed by an annealing step under an O-2 flow at T = 800 degrees C and T = 1000 degrees C. Accurate UV-vis and EPR spectroscopy investigations show the coexistence of isolated Cr4+ and Cr3+ ions as well as ferromagnetic Cr4+-Cr3+ and antiferromagnetic Cr3+-Cr3+ interactions. The strong purple hue is related to the isolated Cr4+ ions stabilized in a distorted octahedral site. This is thanks to the second-order Jahn-Teller (SOJT) effect with a crystal field splitting 10Dq value around 2.4 eV, whereas the 10Dq value is around 2 eV for isotropic Cr3+ ions, partially substituted for Sn4+ ions in cassiterite. Just after the coprecipitation process, only Cr3+ species are stabilized in this rutile network with a poor crystallinity. The isolated Cr4+ content remains high after annealing at 800 degrees C for 2 days especially for the highest Cr rate (2 and 5 mol %), leading to a darker purple color, but unfortunately the Cr(3+ )content also increases for a higher Cr concentration. A lighter purple hue can be reached after calcination at a higher temperature (T = 1000 degrees C) for a shorter time (4 h) but with a lower Cr content to avoid Cr clusters. This is due to stabilizing a high content of isolated Cr4+ species and limiting the Cr4+-Cr3+ ferromagnetic interactions, which are optimal for a 2% Cr content and also cause the color to darken. The key roles of the Cr(4+ )rate and the Cr4+-Cr3+ clusters create local defects whose concentration strongly varies with a total Cr content, which have then been demonstrated to strongly influence the optical and magnetic properties.