I think she'd look amazing in something forest green, to be honest.
But I also think red is her color. Her red carpet gown at the Brit Awards is hands down my favorite look of hers. (The dress she wore for her performance at the Grammys last year was gorgeous, too.) She looks stunning in it, and I'd love to see her wear some more red! She always looks so good in it.
There's also some picture (I'll see if I can find it) of her wearing a yellow top. I think it might have been from her 2012
Vogue photoshoot. Not that I want her to wear yellow, but it's another example of her wearing color and SLAYING it. I do think that black is a timeless, classy color and that it will never go out of style and that she always looks good in it, but she needs to mix it up a little. She looks AMAZING in color and I want to see her wear some more of it!
EDIT: Here's the picture of her in yellow. It's from her
InStyle 2011 photshoot.
I think she'd look great in royal blue, too. I loved her purple dress from the
Q photoshoot, and I think colors in that color range would really suit her too.