Top panels: Total (g + r) flux corrected by reddening (E(B − V) = 0.27) following the Fitzpatrick (1999) reddening law for two regions with well-sampled light curves. Bottom panels: g − r colours (corrected by reddening) for the same two regions with well-sampled light curves. The vertical dash-dotted blue lines mark the observed flux maxima, and the vertical dashed red lines mark the colour maxima (redder colours). The flux and the colours show periodic undulations.