<p>Heat treatment is a widely employed method for improving gemstone color. In this study, yellow-green sphene was subjected to heat treatment in both oxidizing and reducing atmospheres. By comparing the composition, structure, and ion valence of samples before and after heat treatment, we analyzed the coloration mechanism of sphene and identified the optimal heat treatment conditions. The results indicate that the change in the valence state of Fe during the heating process is the primary reason for the color change of sphene. In an oxidizing atmosphere, some Fe²⁺ ions were oxidized to Fe³⁺, increasing the yellow tone of sphene. Conversely, in a reducing atmosphere, some Fe³⁺ ions were reduced to Fe²⁺, decreasing the yellow tone. Under an oxidizing atmosphere, we achieved a highly saturated sphene body color favored in the market, providing valuable insights and experimental data for further research on sphene heat treatment.</p>