"Rit dye more" dying polyester....help?

Question

I dyed this curtain..it was supposed to be black. I know polyester is hard to dye because it's mostly plasticity. 
The first time I dyed it i used just the basic dye, didn't take.
I used the "dye more" for polyester but it's grey not black..
BUT I was wonder if I dye it again it'll be darker?

Answer

i honestly can never get my dye to turn completely black and i’ve used RIT and the packet dyes (the ones you use for a gallon of water) it’s always a dark grey or a blue grey tint

Answer

Why not just buy a black curtain instead of going through all this? The time value of money matters too! Lol.

Answer

Is it think so. Buy cotton if you want it darker.