Temporary Hair Colour

LOL...OK, I grabbed the box, but there has to be eleventy-billion ingredients listed between the colour, the developer, and the conditioner! Is there something in particular you want me to look for?

Incidentally, I truly appreciate your willingness to help!
:^D

My question is two-fold:

1) How do temporary colours, such as Natural Instincts, work? Do they leave a deposit on your hair until it washes out?

2) The reason I ask the first question is this: I have used several different shades of Natural Instincts. When I use one very close to my own hair colour, my hair feels soft, healthy and manageable. However, when I go a shade or two darker (as I did yesterday), it feels too soft and very, very limp. It will not hold a style regardless of what I try to do with it (blow dry with a round brush, curling irons), and I hesitate to use a lot of product because it tends to make my hair limper and oily. I even go so far as to eliminate conditioner from my routine (which I`m not exactly comfortable with) in an effort to give it some "oomph," but to no avail. Does anyone have any suggestions as to how I can give my fine hair some body while this darker shade is in it?

Thanks!