New MOST light curve of FU Ori (top panel) and the ground-based U − V, U − B, B − V, V − R_c and V − I_c colour indices (lower panel) in standard magnitudes, with arbitrary offsets indicated. As mentioned in the text, the MSO data (open circles) were aligned to the standardised SAAO data (filled circles) with an accuracy of 0.002 mag. The grey-shaded area determines the approximate boundaries of Segment II data, as defined in Sect. 3. The Segment I data are shown on the left, while the Segment III data are shown on the right.