I feel like there are some occasions where nail polish is appropriate and almost necessary, however, I'm not super girly. I also refuse to where black nail polish by itself. Are there any colors that are sorta in between girly and not?
I think anything that is not pink, red, or sparkly can look good on both men and women (i don't buy into the whole gender roles thing) if you want a more androgynous feel. A rich brown nail polish is awesome.
I wear nail polish everyday, no matter what. There's always a time for nail polish.
Although I am team feminine, there are some colors that I recommend for you. Red is a sexy color. You could also go for a very dark pink. Or you could get a dark color and add a girly nail design to it.
Dark plum, is my favourite however my nails right now are called "funny bunny" and it's not white but an off neutral white so it's not so stark but always looks good! Pastel blue is a nice colour however it really makes your nails stand out.