One of the tricks little Wolfi Mozart got put through at the child prodigy
showoff fests was playing while unsighted in various way: blindfolded,
keyboard covered with a sheet, I forget how else. He did it fine. But it
surprised and impressed lots of people; probably some very fine pianists
can't do it.

I myself play in the dark all the time, both practicing and performing
(mainly the cocktail piano gigs and some of the church oganist ones). In
the real world darkness is a pretty common situation; it was even more so
before the invention of the electric light bulb.

Judy