Either a light beige or brown would be ideal for the curtains.

Forgot to mention it would have to match the curtains in my living room as well

It's hard to tell from the photos...are the walls grayish? If so, I would consider a splash of color like a soft teal or peacock color. But I can't tell if your sofa is blue or purple, so that may not work.

My walls are gray and my couches are royal blue

check out the colored scarf sheers that you could just drape over a rod. I was going to say burgandy, I love it with grey but maybe something the color of your sofa too. Your sofa would pop. I hope this look isnt out of style because I think it looks so good.