Should I use neutral vinyl placemats if I want to make my food the focal point at dinner?

You are right in thinking that you should go with placemats that are neutral-colored. Bright and overbearing designs will detract from your food (at least until people start eating) so if you want the meal to be the focal point, stick to placemats (and napkins and serviettes) in light and neutral colors. Make sure they complement the tablecloth if you are using one, though, so they don't stand out by being too different.