Not sure if this could help but My first idea would be to do Chocolate and then add blue accents to it, like blue booties or roses or something like that. I will keep thinking about it and if i get anymore ideas I will post them. Hope this can help or spark a few more ideas for you.
OK Ok I was searching the internet and found a cake that looked like a present, you could do this one and have the tag say something cute referencing to the baby theme/shower. I got it from a website called Creative memories, INC. here is a link to there site http://www.yourcakeplace.com/products/bridal_shower/index.php Hope this helps.
I have one in my photos--its sorta aqua and brown--you could probably make a better topper than I did 
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