Spectral slope evolution with heliocentric distance comparing data acquired on 2 May 2015 (r_h = 1.73 AU inbound) and 2 July 2016 (r_h = 3.32 AU outbound) images. The July 2016 data were phase reddening corrected from 93° to 62° using the phase reddening coefficient of 0.055 × 10⁻⁴ nm⁻¹ deg⁻¹ determined in Sect. 4.1 for Wosret in the post-perihelion 2016 observations. Comparing to the original data, we applied a zoom factor of 2 to the May 2015 data, while the July 2016 image was binned by a factor of 2.