Leaving it pastels will allow her to change her room decor more easily over the years. I do the idea posted above of making pillow cases or an accent piece with pop.

A tiny amount of a subdued "pop" might make it more "you" without changing the overall theme.

what do you want to POP? the color you add or the pastels that are already there. To me, making something POP means that you are bringing out the value/presence of what is already there so, with the right medium to dark, the pastels will really pop, which should please the recipient in this case. I'd just be careful in selecting the med/dk fabric carefully...and a little goes a long way. How about a narrow flange around blocks or around the quilt - only about 1/8 inch visible? this would highlight the pastels by giving them a very small amount of contrast to be compared to.

Do you want the quilt to be used by the bride and groom or do you want it to end up as a dog bed, at the local thrift store or as a bargain at the happy couples first garage sale? If it is the latter, then by all means add the pop.

I agree with this suggestion. I usually do a narrow border or make the binding of the same/similar fabric I want to 'pull' from the top vs. making it 'pop'. Usually a less-used/prominent color from the top just so you can 'see' it a bit more.

That will be a very sophisticated and elegant combination. Adding any thing to make it POP will really take away from that combination.

I agree with feline fanatic, if you want them to love it just stick with their preferred color combo or it's likely to end up a dog bed or in a garage sale.

I would not add the "pop" .. if pastels is the palette leave it at that.

How about a compromise? Include a note with the quilt in which you offer to applique something in a complementary color of her choice on the center and/or border of the quilt if she chooses, with an expiration date so you're not fretting over it come Christmas. That lets the bride decide if she wants that added pop or not instead of chancing that it won't be used because it's "missing something".

Since she said pastels, I'd use the light and med, leave out the dark. Then another color of say pale peach pastel would add another color and maintain the pastel. MOB said white which you didn't say you were using. I'd use that rather than dark.

Yes, I am using as much white as the gray/green combined. The wedding is in October.