Super simple error fix : ansi style code 39 instead of 48 for background

[JostTim]

Tested and working on my windows 10 computer.

The right code for ansi background color is 48, not 39. (link to the problematic line) The error was specific when supplying only one numeric value for background color. It was not the case for tuples of 3 numeric values (RGB) as 48 code was already correctly specified for this case.