Fleurzty, its definitely an alternative. Your hair is naturally lighter than mine too (similar to Spirals?), so although you won't achieve a dramatic color change, it will leave behind a reddish stain. A lady on the board hennaforhair.com said to think of "coloring over black (or brown paper) with a reddish orange crayon."
After all of my color (which has dried my hair out!) is grown out, I'll begin hennaing, rather than using cassia. But until then the conditioning, volume and strength that cassia treatments provide is sufficient.
Spiral, I talked w/Catherine and she said that Cassia is not a protein treatment...so thats good news! Last night, after I rinsed it out, the slip was amazing. I put conditioner on it just because...out of habit I guess, but my hair sure didn't need it. I have to say that my hair is a bit more shrinky, but in a good way. It feels denser