In the future if you are looking for something to remove stains from a washable material, try a product called Lestoil. You can usually find it around other cleaners like Pine-Sol.

In my Navy days I have used it to remove stains from my white uniforms. Anything from motorcycle chain grease/oil on the legs, to black shoe polish, ball point pen ink and even when a red crayon somehow got in the dryer with a load of my whites.

Just dampen the material around the stain, put a few drops on to cover the stain and work in by rubbing material together, or if a particularly nasty stain, use a toothbrush then launder as normal. Inspect after wash and if not completely out, repeat the process before drying.