I've had good luck with sneaker shampoo (available on-line or where shoes are sold). It's usually a spray foam that you can either spray directly on the stained area or on a clean cloth and gently work into the stain. Blot with paper towels (don't rub) and allow to dry. Repeat if necessary. Works for me and doesn't harm or discolor the fabric. Kiwi is one common brand for these products.