a) Three-color composite of the images R_c, V_c and I_c (red, green, and blue image channels, respectively), illustrating the spatial distribution of compact ( ≤ 05) sources in I Zw 18 C. The regions C i, C ii, and C iii defined by IT04 are indicated. The blown up version of the central part of I Zw 18 C (lower-right) shows the ionized gas shell in the vicinity of the bright stellar cluster C (cf. Dufour et al. 1996b). b) Three-color composite of R_d, V_d and I_d, of the unresolved stellar emission. The color coding is the same as in panel a). c) V − I color map of I Zw 18 C, revealing very blue colors (V − I < 0) all over the southeastern third (region C i) of the galaxy. The contour corresponds to 25 V mag/◻″. d) Comparison of the spatial distribution of compact and point sources in V_c and R_c (blue and green channels, respectively) with the unresolved stellar background (I_d, red channel).