Will ombre hair color effect my natural color?

So background information: I'm a natural blonde and my hair doesn't take well to color. Even semipermanent/permanent dye tends to not stay in my hair for more than 4-5 washes. My stylist has told me that she thinks she could get the color to stay for longer periods of time if we bleached my hair first, but that the bleach would very likely have a permanent effect on the color of my hair. Since I do really love the natural color of my hair, she has strongly suggested that I not bleach my hair to take full color if I don't want to risk a permanent change in the color. (BTW my hair is a golden-ish blonde and about shoulder length, very straight and very fine)

My question is: if I do an ombre effect on my hair (from blonde to lilac) would I still be risking a permanent change in my hair color? Is it even possible to only bleach my hair away from the roots and leave my roots untouched when creating the ombre? Is the amount of effort something like this would take going to be huge?