lib/colors: update man page

Signed-off-by: Karel Zak <kzak@redhat.com>
dmesg: support colors customization

Signed-off-by: Karel Zak <kzak@redhat.com>
hexdump: add --color to the man page

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: support colors customization

Signed-off-by: Karel Zak <kzak@redhat.com>
cfdisk: update man page COLORS section

Signed-off-by: Karel Zak <kzak@redhat.com>