How do you keep your Blonde streaks Blonde?

[Little Gem]

For quite a while now, I've been itching to put a blonde/white streake in the front of my hair.
However, my hair is dyed red, and everytime I wash it, at least some of the colour comes out, even thought the dye is permanent. I'm terrified I'll end up with a weird orange bit as soon as I hit the Shampoo bottle!

So, I've noticed a few of you ladies have adopted said streak, and I was wondering how you keep it blonde?

All advice gratefully received :) xxxx