We wonder how long it took Lily Allen to paint herself green for her alien costume! This image appears in the gallery:29 Incredible Celebrity Halloween Costumes: The Spookiest Outfit Ideas 9. We wonder how long it took Lily Allen to paint herself green for her alien costume! Picture: Getty/thinkstock 29 images See the full gallery: 29 Incredible Celebrity Halloween Costumes: The Spookiest Outfit Ideas