use light-gray as default color in normal.mod for consistency

use light-gray as default color in normal.mod for consistency

Defalut font color on PC console seems to be light-gray; this is
what user also gets in rescue prompt and what is defined as
GRUB_TERM_DEFAULT_NORMAL_COLOR. But normal.mod defaults to white.
This makes unpleasant visual effect as colors are changed after kernel
is booted.

Use the same color eveywhere for consistency and default to light-gray
as this is also what at least Linux kernel is using by default.