veggie dyes

I'm talking manic panic, SFX, those types. heres the short question- what color do they fade to? I've here conflicting information that its blue or that its brown.

I recently dyed my hair a near black brown and want to avoid using chemical dyes from now on. i want to add a bit of a veggie dye to my conditioner to punch up and deepen the very dark color a fwe times a week, but NOT fully dye my hair with it. I figure that if I 'water' it down with conditioner, if its blue, won't work, if its a dark brown based black, it would. Anyone know or have experience with this? I know the mehtod of adding them to conditioners is used to keep the funky bright colors longer, so I really mostly am looking for if they're blue or brown based.

tia!