OK...I've got an experiment and I'll let you know the results (unless I get some quick warnings not to do it). 

I have bleached blonde hair (level 9), which I hate because no matter what I use, I can't seem to get the yellow toned down (the last color I used was Wella's Princess Blonde - it was nice for a few days, but faded back to yellow).  So, I've decided to go Marcia Cross red!  Now, I'm definitely an amatuer, but I've been coloring my hair for years and have been reading this forum for months.

Here's what I've learned....

1. If you try to dye bleached blonde hair darker, you're likely to get all kinds of weird results - green/grey/pink depending on the base of the color, so you may have to dye it twice using two opposing base colors (i.e., one with an ash base and one with a red base).
2. Bleached blonde hair is porous and the color is likely to take unevenly, so you have to use a filler.
3. Because bleached blonde hair is porous, you should choose a color two shades lighter than the color you want to go to, otherwise the results will be too dark.

I read Wella's instructions for dying gray or white hair and they said to choose two toners - one in the neutral family to darken the hair, then choose the color you want to tone the hair.  You darken it using equal parts neutral toner and water, then color it using equal parts toner and 20 volume developer.  So, here's what I bought:

1. Wella's medium ashe blonde (level 7) to darken my hair.  It has a violet base (since my hair's light blondish yellowy, I thought it would maybe even come out a normal color, although it still could be gray).
2. Wella's red (level 7) I wonder if I shoulda got an auburn instead....
3. A neutral toner.

(I already have the 20 volume developer at home).  I want to be around a level 5 or 6 in terms of darkness.  I'll have to think about whether I want to darken the hair with water or toner and whether I should use a filler for both steps - I probably will.  I also figure I'll have to tone it pretty often since red tends to fade so badly.

I hope it works.  I'll probably try it tomorrow night.  Otherwise, I'll be wearing a hat until I can get to the salon. 

I wish all these hair color manufacturers that sell color to the public would publish detailed instructions for doing things like going dramatically lighter or more than 2 shades darker.  That way, we could all avoid the bright orange (been there) and the green/gray (hasn't happened yet, but I've never gone from light to dark before).

Wish me luck!

Mary

I'd suggest you go for an acidic toner like goldwell colorance...

It does barely any damage at all to your hair, and leaves it less porous than it was before toning.

http://www.sleekhair.com/3133.html - http://www.sleekhair.com/3133.html

You can find a shade chart on that side, that explain all the diffrent shades I'd suggest 8N or 9N or 9NP, good luck. You'll also need to get the special developer for colorance, it contain special ingredients and has extra low peroxide to minimize damage to your hair.

Good luck

Don't go for red, unless your absolutely shure, I'd suggest trying a red wig or something first. Cause once you turn red it's very hard to go back to blonde.

As always, indecision is my middle name.  I went back to Sally's and bought some demi-permanent color.  I got Wella 7N and 8N - my hair is a level 9 on their chart.  It seems like their level 7 is pretty close to my natural dark blonde/light brown color.  I think I am going to do the bottom layers in the darker color and then foil in low lights on the top.  I got a red filler for the darker color, but I'm going to do a strand test to see if I need to first.  If not, I'll use the clear filler.

I gonna go darker slower than I was originally planning.  I still have the red, though, and may end up doing that in a week or so.  If it doesn't work out, I'm not gonna go back to blonde.  I'm not a blonde on the inside.  I'll go back to black.  I've gone from black to copper to blonde during the last 9 months.  Copper was cool, but it doesn't match my skin tone and that's what you get when you try to lighten dyed black hair. 

My hair's super fine, but virtually indestructible.

I'm gonna go for it this afternoon....Yeek!

I have Results!!!

Yesterday afternoon, I went ahead and used the Wella demi 8N and 7N on my hair.  The color took evenly and came out very nice - even without a filler (I did a strand test first and it came out fine).  I did the bottom in the 7N and on top I foiled in the 8N as low lights.  It turned out fine, but I decided I liked the darker color better, so this morning, I foiled in the darker color on top - trying to make chunky highlights.  So, now I have light brown/dark blonde hair with a few light blonde highlights - it's sort of caramel & honey. 

I'm surprised it turned out so well.

I still think I'm going to darken up the highlights on top some more, though.  I may paint on streaks of the 7N  on top.  And I may still go red in a week or two.  I dunno....

So, my advice for those who are bleached/double processed light blonde - the Wella demi-permanent color works very well if you want to go a little darker!  Yeah!