LTV of ρ Cas between 1962 and 2020. Top panel: Median (B − V)_obs versus the reduced JD. The dark blue dots define the dark-blue unsteady median. Red dots represent the photometric observations with an available T_eff value (green numbers). Bottom panel: δ (B − V) = (B − V)₀ – (B − V)dJN versus the reduced JD. Red dots and green numbers are similar to those in the top panel (see discussion in Sect. 2.2).