A scanning device includes a transparent platen which receives a sheet to be scanned. A backing assembly is spaced from the platen by the sheet during scanning. The backing assembly includes a backing plate of a fixed color and an electrochromic layer intermediate the backing plate and the platen. The electrochromic layer has a first state in which the electrochromic layer is opaque and has a different color from the fixed color, and a second state, in which the electrochromic layer is transparent to expose the backing plate through it. A sensor is positioned to acquire an image of the sheet based on light passing through the platen. A controller selectively applies a voltage across the electrochromic layer to change the electrochromic layer between the first and second states.