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Figure 1: Purple undulated contours adjacent to orange ones are perceived as two unknown shapes evenly colored by a light veil of orange tint spreading from the orange contours (coloration effect). The two shapes show a strong figure-ground segregation and a solid figural appearance comparable to a bas-relief illuminated from the top and to rounded surfaces segregated in depth and extending out from the flat surface (figure-ground effect). On the contrary, the complementary regions appear as empty spaces with the appearance of holes (Pinna & Reeves, 2006).