With just a little searching, I found these spools of crochet cotton thread. I think I'll add a strand of white in the center, then use this multi-color for the petals. Or maybe I will make them all from the red, white and blue. As with most things I make, a bit of experimenting will need to take place before I settle on one design.
Look for these patriotic flower magnets in my etsy shop in a few weeks.