RGB image of Holmberg II with H_E red, Y_E green, and I_E blue. Foreground extinction has been corrected and sky subtracted as described in the text (Sect. 4.1). In the top panel, the full FoV of 0.7 × 0.7 is shown, while the bottom panel displays the inner 6’ × 6 ’ region corresponding to the white box in the upper panel. In the lower panel, to the east, there is an extensive north-south chain of H II regions (e.g., Hodge et al. 1994) that harbors the ultraluminous X-ray source Ho II ULX-1 (e.g., Zezas et al. 1999; Kaaret et al. 2004), visible as a triangular-shaped blue H II region at α = 08:19:28.98, δ = +70:42:19.3 (J2000). Also visible as a blue circular structure to the north of the H II-region chain is an artifact dichroic ghost (see also Sect. 6, Fig. 15).