Monitoring of color and magnitude variations on the (u − r,r) diagram for CTTS (magenta lines) and WTTS (blue lines) in NGC 2264 on a timescale of weeks. Each bar represents a single object: the center of the bar is located at the color and r-band magnitude of the object at the median luminosity state, while the amplitudes along u − r and r mark the total amount of variability detected during the CFHT monitoring (i.e., (u − r)_max − (u − r)_min and r_max − r_min  over the 10th−95th percentiles range, respectively). The effects of reddening on the diagram are traced by the black arrow in the top right corner (Fiorucci & Munari 2003).