Need advice on dye colors to make a dark gray

[Redwillow]

Working on an Osha costume from Game of Thrones.
I have a medium gray fabric I plan on using for the robe, but I need to dye it darker to the shade shown in the above pic. It looks like an earthy dark gray to me, with maybe a hint of brown in it.

Doing my test dying, first I tried just diluted black, but it came out with a heavy purple tone to it. So after some research I added dark green to counter the purple, in a 2 parts black to 1 part dark green bath.
It's much better, but still has a slight violet tint to it.
These are my best results so far, with the original medium gray fabric on the left which has a bit of a slate blueish color to it.



So what do I need to try now? I was thinking orange to counter blue in the original color? or should I try to add brown to it? or just add more green?

 

[SMP Designs]

Not sure of your level of dye experience, so sorry if these are things you already know. What’s the content of the fabric - is it natural or a blend (makes a big difference in what dye to use)? Fabric should be pre-washed and soaked in hot water before going into the dye and a liberal amount of salt should be dissolved into the dye bath to promote better absorption and truer color.