I didn't say consciousness but consciousness obviouslly refers to content in awareness. So lets go with that.

An individual's shadow is an unconscious region of the psyche formed by the conscious contents of the ego.

Becoming conscious of your shadow, creates more content. Content creates the shadow. Is there special content that doesn't create a shadow?

The ego is not defined here though so before we being, let's define it with the jungian definition of the ego:

Ego. The central complex in the field of consciousness.

The ego, the subject of consciousness, comes into existence as a complex quantity which is constituted partly by the inherited disposition (character constituents) and partly by unconsciously acquired impressions and their attendant phenomena. [“Analytical Psychology and Education,” CW 17, par. 169.]

So when you say:

So what you know about yourself casts a shadow composed of thing you don't know or don't want to know--the negative or dark parts.

What you know about yourself, including things that you have somehow gathered from the unconscious, casts a shadow yet again, of things that you don't know or you don't want to know (two vastly different scenarios based on the premise of can, or ability, and want, desire). But, clearly consciousness is the ego, from their definition of the ego, as it being the "central complex" and from the definition of jungian consciousness:

Consciousness. The function or activity which maintains the relation of psychic contents to the ego; distinguished conceptually from the psyche, which encompasses both consciousness and the unconscious.

And therefore consciousness is ego and not just that, consciousness is the aggregate of psychic contents which in turn make up ones identity or the ego. So to add content to the conscious casts a shadow, as there is no distinction between what casts a shadow and what does not in consciousness.