I kindof answered my own questions by doing some research.  Thank you Curlgirl for your link http://www.mehandi.com! ; Basically I learned that by mixing the cassia with water, there is no releasing the dye molecule - making it a conditioner that is wonderful for your hair.  If I want a yellow added to my already blonde hair I can mix it with lemon juice or vinegar, leave it overnight and apply etc.  Right?  I also read that it will not damage my hair, only make it stronger and healthier in time.  Is that why everyone henna's?
-cera

Cera, I used Cassia for the first time earlier this month.  Mine was mixed w/water, sunflower oil and yogurt.  No color was deposited and it made my hair shiny and thicker feeling.  I will be using it again soon-probably about every 4 weeks.  I go to a salon and have someone apply it for me, since I have a lot of hair and want even coverage w/o super tired arms!

In April, when I'm finished with "The King and I" I"m going to try the cassia w/acid to see what result I'll get to brighten my blonde.