Concatenated XMM-Newton EPIC-PN light curves for the 17 well-exposed observations of Ho II X-1 and the hardness ratio below (here defined as the (1.5–10 keV/0.3–10 keV counts ratio) from 2002 to 2021 with time bins of 1 ks (left)). The vertical dotted lines were included in order to separate each of the individual XMM observations. Hardness-intensity diagram where the points belonging to the same observation have the same colour (right).