I've colored my hair since my late teens, and it has always been a demi-permanent warm brown (or something in the dark auburn-to-burgundy range), usually with some kind of streaks, either sorta natural red-brown or a bright fuschia/cherry/purple tone.

Now, as I'm getting a fair amount of grey, that is no longer working- the base color isn't taking well on the depigmented strands the first time it's dyed, the red-brown looks weirdly pinkish, not in a good way; the new hair closest to the scalp looks funky but past the first 3/4" looks fine. It's time to change my game plan. I don't really want to switch to a permanent, as I'm afraid those will color everything the same, uniform shade and look flat. I've always done my own color, and would like to continue, but not sure how possible that will be.

So I thought I'd try something different and grow the color out and go with the salt & pepper that's there, plus some bleached streaks to make it more Cruella DeVil, which I could use some kind of lavender toner or brighter purple on. It's not like companies are rushing to cater to the aging ex-punk market. So here's my question to the experts out there. I know I'll have to do something with the warm-brown hair I'll be growing out and have to change to a cooler base shade. Can an ash shade be used over a warm brown without it going all muddy? Is there some trick to making the transition, like a filler, or a permanent color over the demi I've been using up to now? Should I just bite the bullet and go to a pro while it's growing?