Left panel: Hertzsprung-Russell evolution tracks for 0.97 M_⊙, Z = 0.02, α = 1.9 for a standard evolution model (red line), and when modifying the atmospheric boundary condition to account for the presence of χ_s = 20% of dark spots on the stellar surface (blue line). Right panel: differences in effective temperature for a given luminosity between the model with no spot, and the model with spots after the effective temperature has been shifted by a constant factor (1 − χ_s)^1/4.