I like both fabrics. I think the bottom blue might add an extra pop here and there. I have never done one of these mysteries, but I've looked at the posts from last year so I would think you will not have a problem with either fabric.
I am hoping to get the color chips tomorrow, I printed the clue yesterday, and today I start pulling fabrics from my little stash. I will see what is what once I have the color cards. This looks to be fun:-) I even have a storage box out ready to hold everything! LOL