FUV − NUV (left) and FUV − I_E (right) colours as a function of stellar mass for the Perseus galaxies studied in this work and for the Virgo galaxies from the GUViCS data (Voyer et al. 2014; Boselli et al. 2014). Filled green squares (diamonds) indicate Perseus ETGs (unclassified) sources from Meusinger et al. (2020). Filled blue diamonds are Perseus LTGs, while the open red circle represents the central galaxy of Perseus, namely NGC 1275. Purple open triangles indicate Virgo LTGs, while Virgo ETGs are represented by purple open stars. M87, the central of Virgo, is also highlighted with an open red square. Black dashed lines are the magnitude limit curves for each corresponding colour for the Perseus observations. Circular apertures are defined in the FUV band starting with a radius equal to the R_eff in I_E by Cuillandre et al. (2025b). Apertures were adjusted when needed to fully encompass the FUV emission, and checked against the I_E images to avoid contamination, as in Voyer et al. (2014). We refer to Sect. 3.1 for more details.