how to keep ash brown from fading/getting brassy?

hey all,

i just dyed my hair from a medium blonde to "light ash brown" (revlon colorsilk #50), which is basically my natural color.  i did this last year, too, in an effort to grow my natural color back and not have to dye it anymore... but  it eventually faded to a brassy, dark "dishwater" blonde color that didn't match my roots, which is why i decided to go completely blonde last summer. 

now i'm trying to go natural again.  the color, having just been applied a few hours ago, is the exact color i wanted.  can anyone recommed a good shampoo/product i can use to help keep it from fading?  i used john frieda's sheer blonde to keep my blonde hair from going brassy and it worked wonders.  do you think that would have the same anti-brassiness effect on light brown hair (and i'm going to be highlighting it blonde, too, so i'll need a way to preserve those highlights as well)?  i know that since the shade i used was "ash" it SHOULDN'T get brassy, but i know from experience that it does, to some degree anyway.

any recommendations are greatly appreciated!


Edited by Katja - March 05 2011 at 2:54am