Please help with grey hair question, please.

My hair is about 90% grey. My natural color was a dark brown. I have put a permanent, over-the-counter ash blonde on it several times. But I can't get it to come out any lighter than a light/medium, reddish brown. Why won't the grey come out blonde and in an ash tone? I would think that grey hair would take the color more accurately. I know a number of women that cover their grey hair with blonde coloring, and it comes out beautifully. That brownish-red hair is just too dark and harsh on me at my age (64). What am I doing wrong? I do hope someone can help me. My hair looks way too dark and red and looks terrible, once again.

Thanks for any help any of you can give to me!