I found these mobiles at JC Penny and boy are they cute. They both play Brahms Lullabys and my favorite is their design and how they look. I could see this pink mobile be placed in either a white or dark brown crib. This mobile in a white crib would draw attention to this pink mobile which would make it stand out more. A dark crib would tie in well with the mobile as well because of the browns in the mobile and the color of pink which works well with a dark brown.
This blue/grey mobile below would look good with both a white and dark colored crib as well but I would love this in a chocolate brown crib with flowy light grey window curtains. Maybe a chevron rug underneath and other dark furniture in the room as well.