Why is scanner backpanel white?

[paulom]

I am scanning photo prints with an Epson V370 scanner. In photos that have a dark background, like night scenes, I have noticed a light shade along the edge of the scanned image. I thought that could be caused by light reflected by the white backpanel, and tried to scan using a matte black surface as a backpanel. This made the light shades disappear, with absolutely no change in any other part of the scanned image.
So, what is the reason for making the backpanel white?
Are there any other consequences of changing it?

[paulom]

I have found that what I called "backpanel" Epson calls "document mat".
Well, I have made some tests and will give an answer to my two questions: the mat color has a great influence in autoexposure. Maybe not if I set an appropiate marquee, As I am scanning several photos at once for cropping later, using professional mode and disabling autoexposure, the only difference is the light shade along the edges.

[BW37]

Thanks for providing a useful bit of information. I've passed this along to my wife who scans lots of old family photos for her scrapbooking. Just to speculate as to why a white document mat is used, I'd guess that since most scanning is of white paper documents, this is the best choice to both minimize visibility of the document edges (in scans, copies, etc.) and to least effect the autoexposure function, again assuming mostly white paper documents as the sources.

I'll have to try a black background for scanning a printed on both sides, semitransparent (thin) paper document to see if it reduces the "bleed through" from the opposite side. I'm guessing it will, but might also effect the autoexposure output. We'll see.

Thanks,
BW