Etaonsh, may I ask you to leave a blank line between each quoted block and
your new text? Like this:

Foo Bar wrote:
> The horse is white.

No, you foo, the horse is black.

> And I can demonstrate it very easily.

There's nothing to demonstrate: it's black.


Your current style of quoting is more compact, but very difficult to read: I
don't understand which parts were written by you and which parts are
quotations of your interlocutor.

Also, you may wish to check your line length setting. Most people use at
least 60 chars per line; your current setting of less that 40 chars per line
makes very short lines.