ways to grow out grey

I have been dying my hair for 30 some odd years, since I was 13. I have bleached, gone black, put bright colors, etc. Currently, I have bleached the front and underneath (nape of neck) hair. The front has teal in it at the moment. The underneath I haven't done anything with yet as it needs another round of lightening before I can put a bright color on. The rest of my hair that is not bleached is dyed black. May hair is naturally a dark brown, but has about 70-80% grey in some areas. So when my roots grow in, it is quite obvious - at least to me.

If I could color it with the bright colors (manic panic, Special Effects, etc.) I would be happy, but it doesn't stick to the grey hair at all, and then just have an ombre look as I grow out the black. I also know how to remove the black with a color correct (Vanish), but as the hair has been "messed with" too much, it still won't be the grey to match the top and will still have a line. It will be a blah medium brown from being processed.

I look horrible in super short hair, so that is not an option.

Anyone have a suggestion?