There isn't really a way to directly influence how dark and fast your pubic hair grows, but there are some interesting tips and advice you should check out:
How to get your pubes to grow quickly
Unfortunately, hair growth is largely pre-determined by your genes, passed on to you from your parents.
However, maintaining a healthy and balanced diet is conducive to thicker and healthier hair.
Alternatively, you may want to consider a merkin: A wig worn over the pubic area.
You can find more information about merkins on the internet, but just be careful which sites you end up landing on!
Finally, you might find it interesting to know that a recent survey of females in the United States shows that over 90% of women actually trim or shave their pubic hair.
So if you're having problems growing out your pubic hair thick and dark, you might find it comforting to know that the majority of people find that a positive quality!