The "gray background" is really a "bright black" background. The old IBM CGA and successors had a flag for whether to interpret the top bit of the background color as intensity or blink[0]. It looks like Linux used to have it set to blink a few years back[1].

[0] http://webpages.charter.net/danrollins/techhelp/0087.HTM

[1] http://sourceforge.net/p/linux-fbdev/mailman/message/7849329...