I think I would do as already mentioned and find out the colors she will be using in decorating, either the room you think your quilt would be used or the general scheme in their home together and go with that. That being said, none of that may be actually knowable, in which case I would make it with lots of neutrals and add some of the colors in small amounts that she likes but not too bright and not too flowery so he will like it too. Batiks would be wonderful! Be sure to post the pic and remind us of this story when it's finished ok? I'm sure we will all be curious what you came up with.