Our crib is a dark cherry wood, btw.

sage and beige

Oh gosh, Karen, I don't see gray going with that color bedding at all. And, btw, it is adorable! What I see, and as you being a new mother you're probably not up to this project, but how about a white chair rail with beadboard below in the raspberry color of bedding and a crisp white above or vice versa? Also, the beadboard could go up higher, like two thirds on the wall for an even more dramatic effect. And crown molding could be added as well. Or even the raspberry and pale green combination.

I know I am dreaming, just a suggestion. I have two grandsons so I don't get to use pretty girly colors! :))

Look at BM vale mist. It is green, but it is very flexible.

I split the difference between gray and the blue in your bedding set to see what you think. The crib years fly by, so you're wise to be thinking ahead. The art is from:
http://www.etsy.com/shop/pixiepixels

@sam0705, I'm afraid you're right... it is way more country cottage than I had wanted. I got it on a whim secondhand; it wasn't really what I wanted. Maybe I should sell it and get what I want. :-) By the time I decide I'm pretty sure my baby will be in a big kid's bed anyway. haha

What was the look you were envisioning? Any inspiration pics? If it were me I would use the sheet only - you can always use the blanket for tummy time, etc. the bumper and skirt are what look the most country. I wouldn't use a bumper at all and then buy a skirt in a more modern fabric like a stripe or a chevron. Here's a yellow and grey option from land of nod. Then I think you will be good with grey walls and yellow accents.
http://m.landofnod.com/not-a-peep-crib-reversible-skirt/f11787

I'm leaning towards yielding to the butter yellow on the walls. Maybe do wide stripes on one wall with the existing off-white. Maybe just do the stripes on one wall, leaving the existing white color, so that the room isn't overwhelmingly yellow. I do love the idea of using the raspberry color! Very tempting.

I really like the looks here:
http://www.100layercakelet.com/2013/07/29/modern-girls-nursery-from-erin-of-design-for-minikind/
http://www.sadieandstella.com/2012/05/favorite-room-feature-small-shop-studio.html

My baby is already more than 5 months old so we're just about done with tummy time. :-) As much as I wouldn't mind selling the bedding set and getting a different one, I should probably just work with what I have.

Love the inspiration rooms. I see the look u were going for. I think the yellow stripes will be nice. If you do want to go a little more modern you could consider a wide horizontal stripe in the raspberry against the off white walls.
Either way I think if you mix in some modern artwork and other prints like the inspiration pics it will be closer to what you envisioned.

Example of stripe
http://houzz.com/photos/73327

I would go green ,its fresh,its cheerful and its youthful