lualoader: Setup default color scheme if we're using colors

The console may have been set for different colors before lualoader kicks
in; notably, a black-on-white color scheme is not necessarily what we're
expecting.

While here, make color.default() a composition of color.escape() instead of
rewriting the escape sequence to make it more obvious what it's achieving: a
white-on-black color scheme with no attributes set.

Reported by: emaste, whose eyes may rest easily