Here's a simple acorn outline which would be good for applique. The bottom and stem are done in a medium brown and the cap is dark brown. I found this by googling "acorn" using IMAGES instead of WEB from the top bar on the google page.
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http://t3.gstatic.com/images?q=tbn:ANd9GcQqonJ_JDraqKFbo0Nn06kj1FFO5lNelu4N2ufMRSrxx Wc7jwVZNg[/img]
Good luck with whichever one you try.